Hey there

If I cure my vampirism after building the coffin in a player home in Hearthfire, will the coffin still be there?

Thanks

Yes, it will still be there. You just won't gain the specific perk (http://elderscrolls.wikia.com/wiki/Sleeping_(Skyrim)#Vampiric_Blood_Rested) that a vampire would get from sleeping in it. By the way, as you've probably noticed, the Hearthfire coffins can only be built (in the first place) if you are a vampire.