Can yeast in a primary fermentation of wine be used as a source of yeast for new fermentation?
Yes, it is possible to reuse yeast in both beer and wine fermentation - commercial brewers do it all the time for cost savings and batch reproducibility, and although I'm not as familiar with making wine, many sites including this one say it's perfectly fine, as long as the viability of the cells is high enough. 

The yeast aren't necessarily in stress-induced survival mode during fermentation, they're just living (and metabolizing) anaerobically. They may no longer be reproducing, or doing it very infrequently, but they'll remain perfectly happy little buggers (that's a technical term) for quite a while. Give them more food (sugar), and they'll keep fermenting. What eventually stops the process with wine is the level of ethanol rising too high for their comfort. If you were to dilute the ethanol out with water, they'd keep going.

Now, I wouldn't recommend doing this indefinitely (some strains may exhibit genomic instability, etc.), but new batches can certainly be produced with existing pitches.