So since the update to 5.0 I have been trying to install BBM. Every time I tried, I couldn't find it anywhere even though it showed as "Installed". And in doing so, I figured out how to get it back...
Open App World, then My World. Delete the BBM from here and you will be asked to Reboot, which you will do. Once your device is back up, reinstall it from your browser, not the other App Center OR App World. Reinstall it only from your browser at BlackBerry - BlackBerry Messenger
this new OS is great, but its too bad thats there's TONS of issues that only affect a small number of us.... wish it was more uniform and everyone had/didnt have the same problems...