If DB were to buy WCRC and use their own drivers, would they make a profit out of running it (or at least cover all running costs)?
Highly unlikely. There's nothing much for DB to buy (or anyone else for that matter.) West Coast Railway Company Ltd own very little of the rolling stock that they use. Most of it is hired-in from the immediate parent company (Steamtown Railway Museum Ltd) and ultimate parent company (William Smith (Wakefield) Ltd.)
The most recent accounts are for the year-ending March 31st 2015, but in that year WCRC paid Steamtown Railway Museum £1.2M and William Smith (Wakefield) Ltd £406,750 for rolling stock hire. Additionally, it cost West Coast a further £161,000 to hire rolling stock from Scottish Highland Railway Co (another company owned by David Smith), which I am assuming to be the stock used on The Jacobite services.
West Coast are only carrying railway rolling stock assets worth £808,257 as at March 31st 2015. (And, incidentally, pretty much everything that WCRC
does own is is debentured to Barclays Bank as security against all money due or to become due to the bank.)
Why therefore would DB want to buy West Coast? They would be buying a train operating company that currently cannot actually operate any trains and has little rolling stock of its own. It doesn't even employ any staff. They all work for Carnforth Railway Restoration & Engineering Services Ltd - another wholly-owned subsidiary of Steamtown Railway Museum Ltd.