Do Salmon Run matches change difficulty when players drop?

Solution 1:

Yes, the difficulty is adjusted instantly. Specifically, the egg quotas of the current and future waves are significantly reduced as soon as a player drops out. Enemy spawns also decrease, but this is less noticeable.

Salmon Run is intended to be played locally with 2-4 players, so there is appropriate difficulty scaling built in. Ordinarily it can't be played with 1 player, although this does apparently happen to some people online if their lobby times out, so I'm not sure what it would be like in that case.

Note however that having less than 4 players in online Salmon Run means that at least one of the intended weapons will be missing from the field. This can put you at a disadvantage against certain enemy types.