As said the HEGO will not stop engine starting, it can only cause it to lose fine control of the fuelling due to no LAMDA reading, so it will either go into LOS(LIMP HOME MODE) or set value of a hot engine.
If there was any doubt about the fuel supply, just rig up pump to a permanent live so it runs continuously then try and you will most likely find all is ok then, so you would be looking at a fuel pump signal issue.
a said the injectors are not sudenly going to block, and you seemed to have determined it is sparking.
tabetha