Yeah, it's true that he'll be quite old. Still, it's possible that he'll be in power.
The reason why I was thinking of WWII was not so much because of ideology (Sidónio was arguably less fascist than Salazar, he was more of a conservative nationalist than anything else imo) but more because of his outspoken pro-german sympathies (from what I've head, the man would have been very happy if Portugal had broke with the Entente and joined the central powers in WWI). But yeah, I agree that he would probably keep Portugal neutral if he was smart enough (and he was no idiot as far as we know).
Now, if he's dead and democracy is back, then I guess it becomes more likely for Portugal to join the allies (that is, if the allies let them).