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?