I think the big question is and I think we will have to wait for the accident investigators conclusions, is regardless of the decisions that were made that brought this aircraft to an altitude it was, why wasnt it able to maintain 1500ft. There are a number of possibilities, lets explore the more obvious ones and it should be noted that I am not Mojave type rated.
We know an engine was shutdown inflight, because he said so.
1. The operating engine was unable or was not delivering maximum takeoff power.
2. The aircraft was producing excessive drag for best climb performance (ie. has a cowling/locker door been displaced.)
3. Was the aircrafts actual weight less than maximum one engine out IFR weight.
I think these are the key issues that need to be determined.