Give the fluids a go. If Allen perks up he may have a good life for some time to come.
You know that Filou survived for 5 years- and even the 2 or 3 crisis he experienced in his last year didn't slow him up. He loved the Royal Canin diet food and his extra goodies like egg yolk - up to goose fat
If the fluids don't make a difference then of course it would be time to let Allen go.