Is it possible to run rm -rf / without root access?
First off, running rm -rf / is always a bad idea – but you probably know that already.

Second: Yes, of course you can run this even without root. But it wouldn't be able to delete all files, for multiple reasons:


it can only delete files where the user executing the command has permissions to. Those are, naturally, pretty few (except for on shared storage aka SD card)
parts of the file system are mounted read-only (eg. /system). Those couldn't even be deleted with root powers unless before remounted with write access.