not a mirror... hmmmm .. that makes it difficult.... your idea to rebuilt the root disk is a good idea....
so lets have a try:

shutdown your server and replace disk1. make a reconfiguration boot, so that solaris know the new disk and i would do that all in single user mode (boot -rs)
yes you have to ajust the partitions... to get the same try:
prtvtoc /dev/rdsk/c0t0d0s2 | fmthard -s - /dev/rdsk/c0t1d0s2

the second part of ufsdump(M) is ufsrestore(M), so you can rebuild your data... now you have to install a bootblock, there must be a command called installblk (?), i don't know the path to your bootblock but when i will have time i will have a look on monday at my company...

after that step the system should run again......

if you need more info it will come on monday or thuesday so hold on ;-)

greetings pressy