I face a slightly different "locked-in" issue. For me, most of my masters are not PSD but in Lightroom. Where I've edited in Photoshop (no more than 5-10% of images), the results are normally tiff. If the Photoshop editing was trivial and easily repeatable - say, a bit of straight forward cloning - then I save to jpeg, as D800 tiffs are huuuuge. Even after Photoshop, there might be further Lightroom adjustments, so the results are in Adobe-proprietary metadata. I keep it that way so I can go back and edit some more and, like Isaac, it happens quite often. If I want an image for a particular purpose I might find something from 5 years ago or more, and almost certainly I'll want to tweak it.
If ever I face the prospect of not being able to use Lightroom, I'll need a mega-export session to export currently around 65,000 images from Lightroom. That would probably be to Tif for high-rated stuff, and high-quality jpeg for the rest. Several days' work for the computer, but computers like that sort of thing!