This has me totally lost

Hello all

I've been diy-maintaining the family's cars for nearly 50 years but I reckon I'm getting past it now. This latest problem has got me on the run, hence this post.
Our Vectra with a Z19DT engine had been behaving itself well until yesterday evening. During the day I did about 20 miles in it and my wife took it out about 2 hours after I got back, to visit a friend half a mile away. When it came time to come home she started the car but the engine cut out at the instant she put on the lights. Lights off, it restarted and then same again. After that it won't start for love nor money. Battery is sound. Op-com first brought up:
Crankshaft position sensor open circuit
Coolant temperature circuit low input

plus two "unknown" DTC's

I deleted these and since then the crankshaft DTC hasn't returned but the coolant one is always there. When trying to start it I noticed the glowplug light stays on longer than I'd expect.

I've substituted another sensor from a Z19DT and checked connections are clean and wires in the cable "elbow" are intact. I didn't dare poke around with my multimeter, though.

The fuel gauge reads empty. No sign of needle moving. The gauge was reading plenty in the tank earlier in day. On the assumption the sender had conned us I put 6 litres in and went through the "ran out of fuel" routine as Vauxhall describe in the handbook. I could hear the tank pump and I took one of the return pipes off an injector and got a fountain of diesel a few seconds after turning on the ignition so there's diesel getting to the injectors. No sign of firing.
I've checked fuses. Everything else electrical is A1.

Any ideas? I know the crankshaft DTC is suspicious but I can't understand how an "OPEN circuit" DTC could no longer show BUT still cause a problem. Is the injector pump just not up to blowing out air in the high-pressure plumbing after 140,000miles? Would a shot coolant sensor stop the car starting? Is there a way to by-pass the pressure sensor I understand is on the common rail, to bleed out some air?

Any words of wisdom would be much appreciated.