Reveg is strain dependent and it matters how much you trimmed your original plants, how long you let them grow before harvest etc. The less you trimmed your lower stuff the more likely it is you will have luck reveging any of them and the sooner you harvest the better your chances. Sativa's are easy as pie compared with indicas to reveg and since you don't need to grow them all that much before flipping them it's not a bad way to get two crops. Start your first seeds on 12/12 from day one, don't trim the lowers so you have spots for new growth, harvest the buds when ready, reveg for two or three weeks and you are back in business with a bushy plant that will still fit in your room. Indicas I've only revegged if the plant was supper special and I decided I wanted to save the genetics more than I'm worried about smokable bud. then I'll pick it early as possible, take off just the main colas and hope for the best. And even then I'm likely to grow that plant into a mother to take clones from that plant, rather than flower the reveged plant itself.
Although I've put a few reveged plants outside before and that worked out good too but they had a whole season to grow back to monster size before they started to flower. As stated above it's not really worth the time to reveg if you have the same plant available to you in seed form.
And left over buds on reveg plants are smokable it's just that they are usually funky, with the odd flavor and buzz you get from letting any plant flower past it's prime.
edit: And although seeds can be popped right away after harvest and sometimes they will be fine, it's usually better to let fresh seeds dry completely before trying to plant them. So Turnaround on seeds from freshly harvested plants it's quite as quick as people make it out to be either, not unless you want to push your luck popping seeds that might give you some freaks.
