The reason that we might want to upgrade to Integrity is that someday
it will be hard to get replacements or maintenance for Alpha hardware
(DS10ish systems in our case).

I guess that date is probably 10 to 30 years out. Any better guesses?

Anyway, if Integrity sales are poor and it gets discontinued, then
Integrity will have a similar slow death.

Will Alpha really die before Integrity? If not, then there is no real
point in upgrading in order to forstall death.

By die, of course, I mean become unreplacable and unmaintainable.