I just thank god that we live in a time where everyone has a cellphone. Read 'Junky' By William Burroughs if you want to see how fucked up it was to cop back then..One would basically tell their customer to meet them at such and such time over by the corner of something and something street, and then the customer would just hope the guy remembered to show.
Anyway, waiting for a dealer to show up when you're sick is just part of the game. It's how it's been for probably a hundred years or more, and it will continue to be that way unless drugs are legalized and one could walk into their local opium den and order a cup of PPT and a gram of heroin to go.
The best thing to do-if you can, is to always have some kind of emergency meds around, because this shit happens even with the best, punctual of drug dealers . For instance, always have a wake up, or some other kind of comfort med that can distract you somewhat from your withdrawals. This is key for me-I always save at least one bag for the morning, or if I have amphetamines instead, I use those (for some reason dextroamphetamine as well as methamphetamine...well especially meth, can mask opiate withdrawals really well in my case). If nothing else I'll try to make sure I at least have some benzo's on hand (unless I'm waiting to pick up benzo's).
Either way, I think it's essential to have something to wake up to, no matter how small or shitty- as long as it helps hold of WD for a little while longer, or masks them for a period of time, it's worth it, because I'm one of the people that will literally begin to get so sick feeling that I just won't even have the will power to go out and cop unless I have someone who can deliver or take me there by car.