Re: The business of flies
Melanogaster produce the fastest, they're a great beginner fly. Hydei cultures take much longer to take off. To be safe I'd just make fresh cultures every week.
I've experienced crashes, but only when I didn't add enough water to the media and cultures dried out in the winter months (dry air from heating).
I've always felt safer with P. terribilis in that I can feed them crickets (pinheads up to quarter-inch) if necessary, but that's just my paranoia. With a set routine and a couple of extra cultures in case of error, I've done fine over the years with thumbnails, tincs, terribilis, whatever...now that being said, I'll echo what others have said for newcomers to the hobby:
No way around flies, and learn your flies to avoid heartache.
After years of keeping herps that ate crickets as a staple, I actually appreciated the whole fruit fly thing for a good long time.
What to do in case of emergencies depends on where you are and what you're keeping. Have a contingency plan in place beforehand so you don't need to figure it out on the fly.
(See what I did there?)