To answer your first question, there is a tool called 'resize_reiserfs'. I never used it, but it is referenced on the reiserfs home site www.namesys.com
In reply to your last question, if your original installation was entirely in the reiserfs partition, everything should still be OK. Except maybe the boot process needs to be reconfigured.
I don't understand the mount failure tho'. Are you booting with GRUB? I wonder if deleting partitions upsets the GRUB configuration?