Can this crank arm be saved? Here's my drive-side crank arm, from the inside of the chainrings:



First off, those are not chain ring bolts, they are rivets, argh :)

It looks like the crank arm is fixed to the middle of the three chainrings, with the plastic spread out.

If I drill out these rivets to fit on new chainrings, can this crank arm be even re-used? Or is it fixed-on to the middle chainring for good?

My objective is to replace the chainraings, but maybe I'll end up replacing the full crankset.

I can't drill the rivets now and see, because I need the bike every day.
A replacement crank set will likely be your best bet. As once you drill out the rivets the structural integrity (what little it has) will be effected and eventually your new chainring bolts you install may wallow out and deform the holes cause a slight play, from there the slight play will gradually get worse until something snaps under force and you will be right back at this very place. Beyond that i don't know how you would remove and reuse the actual crank arm.

Bottom line riveted crank sets are made to be replaced when they wear out. Could you drill and use it? Probably.. well maybe.. but i wouldn't consider it a wise move. I think you would be better suited to look into a replacement and possible upgrade to one that has removable rings.

After all the time and effort put into converting the old one and hoping it holds you could just replace and forget about it. As others have said in the comments you should also check your chain and rear cassette or freewheel for wear as well. If your chain is worn it will not work as well with a new crank and will cause it to also wear prematurely.