Question
what would cause my sprinkler heads to NOT go back down after running their cycle?

Answer
If it is all or a lot of the heads, it may be that they have weak springs that may be worn out.  If it is just a few, or on one line, it may be that the valve is closing very slowly or is leaking a little bit.  Try adjusting it by opening it all the way, then close it all the way, then open it back up halfway.  If this doesnt work, you may need to dissassemble the valve and clean out the internal parts.  Do this very carefully.