I'm so sorry that you lost your favourite birdie...
Sometimes with the impacted crop they can basically starve to death because nothing can get by.
An antibiotic could help with a secondary infection, but not the impacted part.
Just sending my condolences too! It's always tough to lose a beloved pet and we always second guess ourselves. We just have to do the best we can with what we have and know at the time. Don't beat yourself up...
you asked about antibiotics. i have gotten some at the feed store but not used them on chickens. i would go in there and ask them while you are thinking about it and then you can be prepared for later. sorry about your bird.