I would imagine that, (had there been no revolution,) Tatiana would continue with hospital work for a couple years, then marry and have a small family, yet still continue her nursing/doctoring work.
Olga is always classified as being the independent one, but I think that Tatiana was also very independent-- she just was able to rein in her sense of independence and be practical because she may have thought, "one fiercely independent girl in the family is enough, I must try and be a 'good girl' for Mama because it's best." But if she had been able to become her own woman more, and gone out on her own, Tatiana likely would have been able to get by more, so to speak, in the "wide world" than Olga, because she could handle things better, and "keep her cool" in hard situations, where Olga would have been more likely to loose control. Tatiana was very level-headed, I think. She felt deeply, but could curb her feelings and be sensible.