Hello I have a bowl of acetone with the acetone-soluble parts of salvia dissolved in it. I have the bowl in a saucepan full of warm water, this is to heat the bowl of acetone so it will evaporate faster. Does exposing salvinorin A to heat damage it?

No, it isn't sensitive to heat, but it is sensitive to light.

Could I boil the acetone away because the boiling point of acetone is 50oC and the boiling point of salvinorin A is about 300oC, would boiling acetone be dangerous?

Acetone evaporates very easily at room temperature, especially with a fan in a shallow dish (lots of surface area). Why boil? It sounds very unsafe and very unnecessary.

Do all amounts of liquid eventually evaporate, like if there was 5 litres of liquid in an open container would it eventually all evaporate? How am I supposed to know where the limit of evaporation is?

All liquids in a salvia extraction will evaporate. The only liquids present are acetone and a small amount of water.

Using a fan will greatly speed up the evaporation, but this must be done in a very well-ventilated area.