Quite an interesting scenario, I'll try to tackle the Portuguese side a bit first. I've actually been reading into this lately for a project.
When King João VI dies, it's quite likely that the Regent Princess calls Miguel to the throne, without Pedro around to fashion his compromise. The absence of an active Constitution will make it harder for liberals to oppose him, and indeed it's likely the first years of his reign will look quite a bit like OTL, although without as much persecution of liberal opponents, especially in the countryside. Then again, maybe not, because the persecutions were more about lingering resentments than any sort of official policy.
Now, a lot of the reasons why the Miguelist regime fell was because of the revolutionary change in Europe, with France getting the July Monarchy, England getting a new Whig government and Spain getting a more liberal-inclined Regency facing the Carlists. This made the European powers turn from sympathetic to the regime to sympathetic to the liberals and, when the tide began to turn, openly siding with the liberals. Now, without Pedro, the liberals lose their figurehead, but these diplomatic forces are still at play. Which leaves us with some possibilities:
1) The regime withstands and is able to remain as an absolutist monarchy in a sea of liberal monarchies. A situation that probably would crumble when 1848 arrives at the latest
2) Dom Miguel chills out (or, depending on your reading of the period, never goes full reactionary) and allows for some modest reform to happen, perhaps to the right of the OTL 1826 Charter, but not that different. This seems quite likely, as without the war there would be more liberal voices in administrative positions and Dom Miguel himself never seemed to keen on ruling, and with the death of his mother losing a strong incentive to keep pushing for that. Again, depending on how absolutist this regime is it might fare better or worse once 1848 arrives
3) A liberal revolt, if not directly backed at least entertained by the British and French, removes Dom Miguel from power, possibly if he starts to support the Carlists in the war and pisses out the other powers through that. A constitutional regime would come into place (probably not with the 1822 Constitution, but it's possible too) and the question is who replaces Miguel? A republic seems unlikely in the current climate, pan-Iberism is still in its infancy (and with the Carlist Wars raging and an infant girl on the Spanish throne seeming less palatable), unification with Brazil is out of the question, other dynastic connections are quite in bed with the Miguelist-Carlist camp, and bringing in an European prince... Could happen. Seems a bit of a fragile arrangement, but it's not like Spain didn't have that happen a few decades later (and not go that well, but alas)
Hopefully someone will refute some of my statements here, since that will probably make me note some things I am wrong about for my project too hehe.
I may try my hand at Brazil later, but let's wait and see what other people more knowledgeable about that say first.