Glow plugs are not really a necessary part of a diesel engine's operation. I had a Case tractor for a few years and it had no glow plugs at all. Started like a champ at -2 F. In fact, diesel engines have powered trucks, planes, ships and industry for 100 years, nearly 1/2 that time without this device, introduced in 1946.

It is possible that the system that controls fuel mixture also controls the glow plug cycle, meaning that the problem would be one of defectives sensor(s) or computer control devices.

I think a cracked piston ring, perhaps a craced piston is to blame, but have injector controls system checked first (by the best diesel mechanic you can locate).