Getting rid of pool and what to do?

Definitely! Just fill it up with some concrete/dirt to level out the ground and you can build a deck over it.

make a garden...add sufficient gravel to level out the slope and then some; add amended soil and plant veg and flowers. wouldn't it be nice if there were some sort of paved edge around it already ... if so, keep that and expand it as a lovely garden surround

you should probably check with your building dept. to see if they have rules for filling in a pool. If ok, I would consider finding some clean fill and completely filling it in before building a deck over it.