The first thing I would do is assess the damage.
The most common problem causing a runaway diesel engine is excess oil entering the engine via the turbo charger. A less common cause is the engine over filled with oil. If you caught the engine in time and stalled it, then you shouldn't have experienced any engine damage and a repair is feasible.
Replacement turbo-charger and a flush out of all the inlet pipes and intercooler if you have one. But if you let it run on until it died its death over revving then the engine is toast.
I am no mechanic and a runaway was totally new to me. I know understand what can cause it and how to stop it. Unfortunately it ran till it died. On the other hand the value was probably £2600 (not including the system and other kit, just the van). I was wondering whether to change or not given I have only 5 years to go, but it needs a new rear axle as torsion bar has gone and maintenance has crept up over the years. In all honesty I probably needed a replacement anyway and this has just forcced my hand.