If your issue is Edit In not working, rather than the Camera Raw plug-in missing, then try these things:
"Edit In Photoshop" command missing
Lightroom FAQ (Frequently Asked Questions) (edit in stops working)
Someone else said that they were using Smart Previews and not originals and the Edit In fails, meaning you can't use Smart Previews with LR with the originals disconnected and expect to use Edit In PS.