I haven't tested the rivets yet, but they feel very solid. However, they are aluminum; if they failed I could always get stainless steel rivets to replace them.
I tried the expansion bolts, but never could keep them from wiggling around - they never felt solid. Even tried epoxying them in, but couldn't get them as snug as I wanted.
I threw away the stock grips, but as I recall, I think you could have reused them.