How do you explain to the fire department that oyu are making players wait in line to exit the room with the fire alarm becuase oyu want to collect things from them as they leave?
Better yet who do you call for the bail money when you are arrested for impeding people from leaving in response to an alarm?
Yes, this, exactly.
Everyone, please take out your copy of the rule book and reread carefully rule 1A.
In the present situation, we are discussing a possible emergency in which life and limb may possibly be at risk. This is absolutely no time to be worrying about rule 15A or trying to collect scoresheets before players exit the building. Yes, the TD should ideally have told the players to leave everything, including scoresheets, behind. However, how many TDs have rehearsed their announcements in case of a fire drill?
So, sometimes, crap happens. Now, the TD uses common sense to figure out what to do. If the round had really only been in progress for five minutes, I could see restarting the round being a reasonable solution. (As far as schedule concerns go, those are probably already out the window considering the time needed to evacuate the building, wait for the fire department to deal with the situation and give the all clear, and get everyone back to the playing room.)
On the other hand, suppose we didn’t restart the round. If the concern is that players would have taken the scoresheet and analyzed with an engine, wouldn’t it be possible that someone else might have noticed and said something to the TD? As pointed out earlier in the thread, we still have a mix of honorable players (I choose to believe this is the majority) and less than honorable players. If this is true, I’d prefer to believe the honorable majority would serve as a check on the others. Could a player get away with it? Sure. On the other hand, how much would engine analysis help in a G/55 d/5 game five minutes into the round? Higher rated players are still likely to be in a book line at that point. Lower rated players will still be likely to be in the opening, and frankly any engine help in the opening will likely be irrelevant once the players reach the middle game.
My personal anecdote: At the chess club where I direct, we have monthly tournaments with one round per week. At the time this story happened, the time control was 40/90 SD/30 d/5. One night, about 2.5 hours into the round, the fire alarm went off. I immediately instructed the players to stop the clocks, leave absolutely everything behind, and exit the building. I didn’t know at the time why I did this, but I also waited until everybody had exited and then closed the interior doors to the playing rooms before leaving the building myself. (Later, I realized that was deeply ingrained training from observing fire drills when I was in elementary school. I had consciously forgotten that the teachers would make sure all the students had left and then close the classroom door behind them.) As we were milling about in the parking lot waiting for the fire department to do their thing, the club president looked me straight in the eye and asked “so what do we do if we can’t get back in the building tonight?”. I looked back at him, thought a bit, and said “I don’t want to be a TD anymore.” 
So far most of the responses address what could have been done to prevent the issue of players leaving with their score sheet from occurring. While that’s certainly worth looking at, it doesn’t answer the question of how to proceed once the initial error has occurred. A couple of options that immediately come to mind are:
Personally, I don’t think there is a perfect solution, but lean toward option 2. However, I would be interested in other people’s thoughts/reasoning.
My reasoning:
Option 1 guarantees impact to some games. Even though only 5 minutes have elapsed, some player may have already established a decisive advantage. On some of the lower boards, there may have already been checkmates or pieces lost. On higher boards, a player knows how his opponent might respond to a certain opening and decide on a different one because he’s not comfortable with the line that was played.
Option 2 opens the door for cheating and accusations of cheating. However, I believe most players are honest and those accusations could be addressed on a case-by-case basis. The impact overall seems to be less than restarting all of the games.
Option 3 may be viable. It probably impacts fewer games than option 1. It still has the disadvantage of potentially forcing someone with a favorable position to give it up because his opponent took his score sheet with him.
Based on the time of the OP, it looks like it was round two of a non-US Chess event with a lot of significant mis-matches in the pairings. I don’t know whether or not there was a groundswell from the coaches favoring either a re-start or a continuation.
True…it is a different animal so I’ll revise the question. 
What would you do in a US Chess rated event?
Under the conditions stated by the OP, with less than 5 minutes off the clocks of a Game 55, d5 time control, the TD should restart the games from the positions on the boards and the noted clock times. If the clocks were turned off, take the elapsed time and split and deduct it from the clocks. Depending on the amount of time the players were out of the room for the emergency, you might have to shorten the next rounds by an appropriate amount to keep on schedule and finish the event on time. As to any alleged cheating, accept and consider claims and evidence in order to make a ruling. There will likely be few if any claims.
There is another option to consider:
Treat it like an adjournment (even though you didn’t have a sealed move in place) and not worry about analysis. Analysis is legal during adjournment - rule 20F1.
It might not be the best option necessarily, but it’s a practical one at least.
WEll, when this happened to me twice in one day of a scholastic 4 round tournament, we restarted the games as is when we got back into the room. We had to deal with some folks who forgot to stop clocks and on those we split the remaining time from clocks that had been turned off.
I did tell folks to leave behind the scoresheets, but not everyone did. And some took their Monroi with them as they didn’t want to leave it behind. I didn’t have time to go out and owrry about all that as I was tryign to match up kids with coaches and parent who legfrt onthe ther side of the building and find coats etc for the kids so they didn’t feeze on a day where the high was around 30.
If they were doing nay analysis outside in the cold in February in the crowd then, well, they just did.
The fire alarm was set off by dust from construction in another part of the building.
Remember the OP stated that less than 5 minutes had gone by since the start of the round. Likely most or all of the games had not gone 10 moves. On the other hand with less than 5 minutes of elapsed time gone by, having a score sheet in hand did not likely help anyone. Also, with less than 5 minutes gone by why bother restarting games rather than just continuing?
Larry S. Cohen