But this is nothing compared to the time from 10^20 to 10^100 years where possibly trillions of God-like entities will be slowly disabled due to a increasing lack of resources. This is comparable to suffering from Alzheimer's, just much worse, much longer and without any hope.

A different (more likely?) scenario is that the god-like entities will not gradually decline their resource usage--they'll store up energy reserves, then burn through them as efficiently as possible, then shut down. It will be really sad each time a god-like entity dies, but not necessarily painful.

Actually, if evolutionary pressures continue (i.e. no singleton) it seems fairly likely that usable resources will collapse suddenly, and resource starvation is relatively brief. Right now, we have an energy diet from the sun--it only releases so much energy at once. But future entities may try to break up stars to use their energy more efficiently (solar fusion is highly inefficient compared to possible levels).