How would you call it?

[Newbie Scott]

I am a first year ump and I have a question regarding proper mechanics. Last night I had a force play at third where the runner beat the throw but slid past the base. My question is do you call the runner safe at third right away even though he slid past the base and then call him out if he gets tagged or do you wait to see if he gets back to the base without being tagged out? Would you approach it different if it wasn't a force play?