If after you have the 50 totems and you have all the puzzles... what next? Let them live on into infinity? To what end? Just a question.

I stopped playing 1 and 3 for the same reason. If you have everything. and you can never be better. What is the point?

Start a new game on a harder difficulty level.
Keep on ringing the gong. (That thing can pick up your tribe, shake it like a snowglobe and turn it on it's head.)

and do you have the various collectibles besides the totems? makes fr interesting decorations on a certain building as those sets are completed

Or even use a simple MOD and change the scenery a little...

What I like to do is keep my completed game for reference - to see what the various puzzles and collectibles look like when they are complete.

I make sure the tribe is ok and self sufficient (with doctors, parents, farmers etc.), maybe check back on them every so often.

Then start new games and play them differently - like buying the techs in different orders, seeing how long I can go before collecting food, maybe concentrating on breeding and building instead of doing the puzzles all right away, making a tribe with one colour hair....

There are countless ways to play again and make it new. I've got all three games and play them over and over again. Just because you've completed it once doesn't mean that's it and you need to move on!