Only your employer and the trustees of the pension scheme can decide on IHR, and it depends entirely on your contract of employment, and whether there is even provision for such a thing.
As far as the state is concerned, there is no such thing as IHR, and it’s entirely between you and your employer - it’s got nothing to do with PIP, and there is no provision to start collecting your state (i.e. non-workplace) pension before normal state retirement age.
The only way IHR will affect state benefits at all is that if you are on means tested benefits, any income may be taken into account, and may lessen your entitlement. That would include drawing a work pension early because you’ve retired due to ill health.
PIP’s not means tested anyway, and is in fact available to people who are still working, so your employment status has nothing to do with PIP - or shouldn’t have. Paradoxically, although there is no barrier to claiming it whilst working, they may try to use the fact somebody still works as evidence they cannot really be very disabled. But other than that, there’s no connection. PIP’s only concerned with whether you meet the disability criteria - not with how much money you have, or whether it comes from work, an ill health pension, or anywhere else.