Well, in either case, readers should know how to properly punctuate. And they should know that questions marks do not belong in a sentence (in Spanish or English) that makes a declaration of doubt, which this one apparently, based on the order of the words, does.
There is another possibility:
Oigan, chicos. Nos quedamos sin bolsas de basura. No sé... ¿De quién es el turno de comprarlas?
In this case the "No sé..." is an unfinished thought.
It's never to late to help someone avoid a mistake they may make by reading a thread.