Petrol is available all the way till Sost. The only long run without any pump ie over 200kms from Sost to Khunjerab pass and back. Your concern should be easily manageable.
Please keep in mind that when we go as a group we face all problems together which allows us to take care of such issues easily. Once I remember there was curfew in Gilgit and trucks were not coming to Sost which left me stranded without diesel there. Ultimately we borrowed diesel from the military which enabled us to return. Such things do happen occasionally.
We plan to finalise the dates on our next GTG with input from all our members considering their conveniences. My guess would be late May, Inshaullah.