Funny, the exact same thing happened to my computer case. I wonder if we have the same case? Got a link to a picture of the case?

My solution was to glue them in place with RTV silicone. My case was designed in such a way that you don't need all that air under the tabs, so there was enough flat surface area to get the silicone to stick and keep the tabs in place decently. I put just enough silicone in place (not too much) so that it was just compressible enough to allow the tabs to push down a tiny bit, just enough to get a reasonable "snap" action. I now take the cover on and off regularly and it still works. The snap is not as crisp as the day it was bought, but it's enough to hold it in place.