Could you make an effort when writing your posts? I don't want to be annoying, but they aren't most easy to read. Thanks.
First, I'd point to you a
very similar thread you made some months ago, and
another recent one.
Was it possible for some roman general or a group of romans to see that the WRE was beyond repair and set up camp in yours truly Britannia. Pod after the roman withdrawal.
Then the answer is in your post : after the roman withdrawal, you didn't have a roman army to speak of, meaning no general, critically when early Vth century WRE was far from being "beyond repair" (it really began being so by the mid and latter part of the century).
That said, if your question is : could a post-Imperial state could exist in Britain in the Vth century, then yes pretty much.
Critically giving that it was what happened IOTL : Saxons didn't pop up and conquered all the island the moment the province was abandoned, and while the provincial structures vanished (being based on imperial authority) the Britto-Roman cities/tribes were maintained and formed entities of their own.
Having, however, an unified entity defining itself as Roman isn't much likely.
As I mentioned you before, the identitary features were the pagi, the tribes. Not really a sense of romanity that wasn't much present past the South-Western cities, and virtually absent from half of the province.
But if it did occur and a roman state was formed how would the rest of the event go woul the Saxons be successful
The Romano-Britton structures were particularly divided (even if some form of high-kinghip may have existed in some regions, as Riothamus name, or rather title, seems to imply) and, after the Roman withdrawal, in need of fighters against Pictish, Gaelic (and probably Northern Britons) raids : Saxons simply came in handy on this matter.