Could T'Pol still be alive during the TNG time period, since Vulcans have a life span of over 200 years?
T'Pol was born in either 2088 or 2089, because she tells Trip on her next birthday she will be 66 years old "Zero Hour". The Enterprise D's plaque says stardate 40759.5 (2363). That would make her 275 years old when Picard takes command of the new flagship. It is unlikely she lived to that age.
In the alternate reality seen in "E2", where the Enterprise crew was thrown into the past and then later the crew met the current Enterprise, T'Pol was 187 years of age, and was looking rather worse for wear.
T'Pol also suffered from neurological issues as a result of her exposure and later addiction to Trellium-D. That probably didn't extend her life any.