Hello, experienced traveller, inexperienced in Indian transfers here, can you advise!

Friend currently on delayed AI 130 (LHR-BOM) is connecting thought to CCU - had plenty of time to connect, but now delayed inbound means that his connection to CCU is 55mins (gulp) as leaving 2 hours late.

At LHR they have issued him his boarding pass for onward flight (all one PNR) but refused to check his bags through to CCU. Is this normal??

What's the procedure for this? As per Wiki

"INTL-to-DOM transfer

Practice is similar to what you may find at major airports in the world such as JFK, LHR, etc. You have to go through immigration, collect bags, go through customs and then TURN LEFT upon exit from customs towards transfer area. DO NOT GO STRAIGHT into Semi-controlled reception area.

It is best to have entire reservation on single PNR to avail of better baggage allowance."

Where is he dropping his bags in BOM - is there a clearly marked 'Bag Drop' in the transfer area?

Also, estimated chance of making connection? Bit worried as the only other AI flight BOM-CCU tomorrow is 12 hours later and showing 100% full. Would AI rather make him wait 24 hours, accommodate him, or stick him on another airline to reach his final destination?

Thanks for all help in advance!