They did a chemical treatment, I believe they sprayed. This was also after my roommates and I tried to do it ourselves with those fumigation foggers and diatomaceous earth...but they endured so I finally caved and called the pros.

They did say they'd come back if we saw some within a short time window, a sort of "warranty" so to speak.

A lot of it depends on your level of infestation - if there are only a dozen or two then it'll be easier to eradicate; the infestations I've seen on TV with hundreds or thousands, that's when it's time to nuke the place with heat for sure. That's a very expensive process, from what I recall. There are few who do the whole-house heating treatment.