If UK stack is likely to only take out Japan slow moving ground units and a plane or two, then no, I think it’s a bad idea to stay there and get wiped out. Most of Japan’s slow moving units at that point can’t do much of anything for awhile, although they maybe could chase the UK-India stack wherever it goes.
But an evacuating UK-India can go trample out the Axis in the Middle east and/or go reinforce/help in Russia or the back side of China.
Again, if UK-India stack (including some aircraft) is just going to sit there and kill a dozen or so slow-moving Japan units and a plane or two to AA fire, that’s a terrible trade for the Allies. And the remaining Japanese units can flood west anyway.
I would think India should only take a stand if they have a good chance of taking out several good (mech/tanks/airplanes) Japanese units, in which case they may have a chance of doing a lot of damage or even outright holding.
You don’t want the Axis player to know you plan to evacuate India no matter what, because then they don’t have to send as much at India and can focus on getting 1 more VC and the win. Once India falls, of course, the Allies have the problem of being 1 VC from a loss and having to defend both Hawaii and NSW every turn until a VC can be taken back
So as far as having a “strategy” to evacuate India, like you intend to move the India stack to the Middle East or Russia at the first good chance, well you’d better have the USA focusing on Japan from the beginning of the game (which a lot of players actually do, these days)