To be fair, the saucer has enough long-range communications ability that it's unlikely they'd be stranded forever. Just until another ship could get to them. Even if the saucer didn't have the capability for such communication on its own (unlikely), at that point I think it would be standard procedure to send a communique to Starfleet when the decision was made to separate the saucer.
Non-canonically speaking, taking a hint from "Destiny", in an absolute worst-case scenario, as long as the saucer had impulse drive it -could- get up to relativistic speeds to rescue its passengers, though obviously there could be some significant consequences. But they'd be alive at the end of it.
While the saucer having the ability to cruise at warp would resolve some dangling episode inconsistencies, I don't believe it was the writers' intention that the saucer have warp drive, nor was it ever mentioned in any episode, nor would it be consistent with the saucer's appearance (have we -ever- seen a warp-capable Starfleet vessel lacking nacelles of some sort?), so I'm forced to conclude that instances of the saucer appearing to have warp capability are holes in the story more than anything else.