Question on failure during cluster operation

Question,

I am wanting to run a cluster on the main table in all of our 200+
databases. However, my manager wants to know what would happen if we suffer
a major failure while the cluster is running. If I am running a "cluster
chosen_index on main_table", and the server crashes, would the database
come back up (assuming the crash did not corrupt the database drives), or
would I be looking at a restore and roll forward?

I am very confident in the cluster, and have seen it improve our
performance, but my boss is still a bit cautious after all the server issues
we had on our old servers and I don't know for sure the correct answer. I
believe that the database would self recover like it does 99% of the time,
and we would be back up running in a few minutes, but I need to know for
sure.

So, what am I looking at if there is a major failure in the middle of a
cluster operation?

Thanks,

Chris

RH 4.0
PG 8.1.3