A manufacturer cannot enter into an agreement with an independent to carry out warranty work - the rest of the franchised network would be, quite rightly, up in arms. If Craig and/or Lotus wanted to approach each other and put a formal agreement in place that would be another matter. There are garages out there who are authorised repairers for manufacturers without being full dealers (ie no sales) so it is possible.
Having said that, warranty work is a poison chalice for garages - it doesn’t pay as well as private work, there is a danger of not being paid out if the factory finds fault in the repair, and then there are warranty audits that can cost thousands in claw backs for any errors found. How many independent garages would want to take that on?
It’s also worth noting that Craig’s departure from Murray’s was far from amicable.
Apparently an announcement from Lotus regarding appointing a new Scottish Lotus dealer is imminent. For the sake of Lotus and Scottish Lotus owners I hope this is true. As you say the current situation is far from ideal.