i have had the exact same problem before, i ended up ordering a replacement from my LFS
for about 18bucks and using silicon to secure the new one back in place, it took about an hour to remove the old, clean the edges and replace.
putting in a glass brace is a good alternative if you don't want to go through all the work. strength will depend on how tightly the glass fits into place, and how good your silicone application is. but if you get the glass cut to the right size, clean all the edges well, and put down a good amount of silicone you shouldn't have a problem.
going with a plastic brace would be the best idea, there will alot less questions or concerns in the long run. if you do go with glass, just make sure every inch of the tank and the glass brace are cleaned, and try to use a pair of rubber gloves when applying the silicone. cleaning is the most important step.