if your opponent stops keeping score after a few moves are made should you contact the TD?
Assuming it is a section that requires keeping score and is not at a point in the time control where keeping score becomes optional, you can contact the TD if you want to. One reason you may not want to is that your opponents gives up the right to easily claim things that require a valid scoresheet, such as three-fold position repetition, time claims in non-SD time controls, 50-move claims. I’ve often been quite willing to let my opponent play without keeping score for those very reasons.
How the TD handles it may vary. One simple option is to keep assessing time penalties until the player it down to five minutes (where score-keeping becomes optional in an SD time control). The player has the right to borrow your scoresheet (during his time) to bring his scoresheet up to date, and must return that scoresheet before hitting the clock.
Some TDs will give warnings and then forfeit the player.
Some TDs may not do much at all.