Rescues will be possible by other locos but will require an emergency adapter fitted to the loco. The train generally then has to run at a reduced speed, as it’s then no longer ‘through braked’ examples being when ECML 67s have rescued 365s.
Or as the 73s and 92s retain buckeyes you could use the ‘failed’ loco as a translator (you can set them up with dellner one end and buckeye the other)
Presumably the drawhooks would be more useful for another loco to couple rather than the buckeye? (Do any 92s actually have a buckeye in fact? Converted or otherwise).
I was going to ask if the loco can act as a barrier in this way and still provide brake continuity. If so, then I guess that if (emphasis on both 'if') the 73s prove to be a problem but still retain the ability to provide head-end power, then using a 66 up front for traction (as they've done with the old stock in the past) might be the most cost-effective solution instead of converting more 73s.
Obviously it’s preferable to have a 73 or 92 rescue as they are fully compatible but that won’t always be possible. I presume 57/3s with Dellner couplings could rescue too?
I think it's been mentioned before that the Dellners on the Mk5s are at a different height to those on the 57/3s, so no.
It's a bit like the ridiculousness of Apollo 13 where they needed to literally fit a square peg in a round hole because they ran out of Carbon Dioxide filters on the lunar module (round) but had plenty for the command module (square).