Can you? Yes.
Should you? Up to you. Sorgon's point was valid, but you can break the heatsink loose with some pressure without damaging anything. Mix it a bit weak if you plan to. Guessing you won't be needing to upgrade that socket 7 again though anyway.
Didn't need a huge amount of pressure for those, I'd try epoxying the tab back into place if you have it. Or "ghetto" as the kids these days say, run a short screw in to use as a tab, just don't get into the wiring.
Depending which side you broke, there are a number of cheap heatsinks (Chrome orb comes to mind) which use all three (or were there only two on that socket, can't remember) on one side, just use the middle one on the other side. So may or may not work, but a thought since a chromey costs less than an AS adhesive kit.
Heck, for that matter I'd just put some heatsink compound on, run a bead of regular epoxy around the edges, set a book on it until it dries and call it good. But I'm cheap. Nevertheless, would work.