As ever some novel thinking but let me try and explain why it's not a great idea.
Firstly, SRB does not run VS, indeed he has very little to do with the company on a day to day basis. There actually is room for more than one long haul airline, the UK is one of the biggest travel markets for long haul and VS has done well without killing off BA.
The reason France only has one is more to do with politics than market forces! Virgin ATLANTIC does not go anywhere near the Middle East for most of it's passengers. Indeed the short haul operation is overdue and is needed to shore up the home market.
As for VS buying BA? That's the most interesting comcept one yet. Much of the profitability at BA comes from the ATI agreement with American Airlines. There would be huge competition issues if somehow BA took that agreement into STAR or massive loss of revenue of they had to leave it behind to merge with a much smaller operator like Virgin.
On your other idea
this will mean VS will pull out of all routes that BA also serve, while launching new routes to destinations not served by either airline
This would close VS. Every single route from LHR has a head to head with BA, that's where the money is. To move the entire operation into new routes would be financial suicide not to mention massively ****ing off their loyal and frequent fliers. Neither idea has wings IMHO.