I wonder how far this can go with considerable distance between Pak/ Bangla, not to mention our sordid history. Indian investment in Bangla is not easy to reverse.
There is hardly any "Indian investment" in Bangladesh left anymore. I am guessing you're driving at the infiltration of India-friendly personnel within the armed forces.
They are being purged and jailed daily. Or have run away.
The Bangladesh army, navy, air force all have intelligence apparatuses and they are fully capable of weeding out traitors from their ranks.
Will Pakistan lose out with an additional ten divisions (soon to be twelve) in the East?
Saying otherwise is insulting and rallying against the strategic overture Pakistan and Bangladesh are both making toward each other - irrespective of incumbent govts. This needs to happen because it will make both nations stronger against adversaries, both militarily and financially. It is plain to see at this point. Pakistan's and Bangladesh' adversaries have already decided on this course of action.
All mature people in both Pakistan and Bangladesh understand and want this tie to develop.