Also you need 2 crew for TP operation. PT6 engines and twotters are used for 20-40 sector days all over the world.
I can't see the engines being the whole problem. Multi crew, hot sections, twotter is a sort after aircraft so purchase value is quite high as well. They are worth more than a Jetstream. And an EU mod spec will be worth more again after you have fitted TCAS TWAS and all that other stuff.
Tri islanders very few want the things apart from 3rd world country's. They now have problems with them as well with avgas going out of fashion.
Oh and here is the AAIB report
Air Accidents Investigation: BN2A MK.III-2 Trislander, G-BDTO