So..
If The Damned are the leaders of the movement then Gothic Rock will have more exposure.
If The Clash are the leaders of the movement then the diverse elements of their sound may create more eclectic off-shoot bands.
I think it's a tossup between them two..
Unless Lemmy Kilmister forms Motorhead with a more pronounced Punk Rock influence? (shedding the Metal side obviously). It's a long shot, but hey! Butterflies are little bastards...
Maybe if Proto Punk bands become more popular in their lifetime? MC5, Stooges, New York Dolls etc.
Addressing your points one by one..
* If The Damned lead the UK punk movement, the chances are that they'll either lead it into goth or a new wave of psychedelic music. In OTL they covered Jefferson Airplane's 'White Rabbit' - and then there's this track the Captain Sensible wrote, which sounds a lot like Syd Barrett's Pink Floyd:
http://www.youtube.com/watch?v=aGFLVRB3Srw
Basically, if lead singer Dave Vanian chooses their direction, it's goth.. and if Captain Sensible chooses their direction it's psychedelia with a fair bit of whimsy.
* If the Clash lead punk, you probably either get punk mixed with classic rock (which would be Joe Strummer's influence - he was in a pub rock band after all) or Funk/early rap (courtesy of Mick Jones). They both had a common meeting point in punk & reggae, but you just have to look at their post-Clash careers to see the artistic differences.
* You raise a good point with Motorhead - they are an outside bet here - chances are if actual punk never happens in the UK, then they'd gain the most out of it because of their attractiveness to the no-BS loud-fast music fans. (a perfect antidote to disco, easy listening & prog rock)
* Dunno about proto punk bands - I thought the original brief was to prolong UK punk, but sure there's potential there for something to strike success earlier. Whether it's the Stooges not succumbing to self-destructive drug use, or the New York Dolls becoming the American Rolling Stones instead of Aerosmith.. feel free to offer your best possibility here.
I personally would love for it to be the Modern Lovers - their geeky spin on rock appeals to a vast untapped market just waiting for the right band - in OTL it's Talking Heads & Devo who got there first, but the Modern Lovers had a romantic bent that never fully emerged in popular geek rock until Weezer hit it big in the 1990s. And they could have got there about 5 years before Talking Heads and Devo, if only Jonathan Richman had not been so 'difficult' with everyone at the time.
Eventually, I think it's inevitable that the smarter punk bands go post-punk (or 'art-rock'). There's a long history of leading-edge punk bands broadening their sound - from the Stooges getting a saxophone on 'Funhouse', to John Lydon forming PiL, to Black Flag slowing it down on side 2 of the 'My War' album, becoming the first progressive punk band..