If we run out of GS drugs and are still waiting for a new delivery, is it possible to halve the dose on a given day, instead of exhausting all the doses and missing 1-2 days?

Yes, this is possible as an alternative to not providing treatment. But it may be better, based on the half-life of GS in the blood, to give the full dose every other day instead of half the dose every day. However, like skipping doses when the drug is available and significantly changing the time of day for injection, this is something that should not become a routine practice.