As for the stability of Diamond... have you seen what's going on with Mooney? Sadly, the only companies you can count on right now are Cessna and Cirrus. Everything else is a gamble - it even looks as though Eclipse will go under.
Indeed but there is a difference between buying a new design plane and buying an older / established one.
The former would be a major problem if the manufacturer goes bust - lack of warranties for a start, and if it is a slightly unusual type with unusual parts (like Thielert engines) then the plane might actually have to be scrapped.
The latter is a lot less bad because what matters then is whether the spares operation has value as a business, and most spares operations have such a huge value that their future is assured.
I fly a 2002 TB20 which has been dead since 2002, but the spares operation will always go on, and the whole plane is easy to work on, and all the bits of relevance (engine and accessories, avionics, electrics) are standard American parts anyway. Importantly, there is a large base (c.2000) going back to 1979 so there is a sufficient demand for airframe parts (which aluminium planes past c. 15yrs start to need) and this keeps the spares operation in money. Nobody buys Lyco engine parts from Socata!
I guess Mooney would be in the same category - a huge and well aged base generating a constant demand for parts. And it is a bog standard piece of aluminium with American avionics and an American engine; all off the shelf items.
But if Thielert goes bust (very likely) and if Diamond were to also hit the rocks, the existing diesel fleet would be doomed because it is not likely that the TC owner would get a new engine certified. But obviously it does depend on when (if) anything happens. Diamond must be getting close to having the new engine sorted, certification wise if not field tested....
You really can't blame Diamond for the problems at Thielert. Curiously, there was also a stand at the Expo showing the Thielert engines, under another name (I forget what) with "manufactured by Thielert" underneath.
The interesting thing, having read some summary of the events at Thielert as reported in the European press, is that the Thielert issues (the fraud, etc) were well publicised in Europe years before they appeared in the UK press. Obviously Diamond were aware of them from day 1. But Diamond's business is selling planes! They obviously made an early decision to cover their options and quietly develop another engine ASAP.