Can ILR granted in 1978 be resurrected?

My partner’s parents lived in the UK in the 1970s. Her father arrived from Nigeria in 1972 as a student on scholarship. My partner and her immediate older sibling were born in the UK in 1975 and 1979. They are both British citizens. Her parents obtained ILR in 1978. The parents returned to Nigeria in 1979 and did not return to the UK. My partner and her sibling returned to live in the UK in 2004 and have remained here ever.

Sadly my partner’s father passed away earlier this year and since then we’ve been considering if it’s possible for her mother to come back to the UK to live with us and her grandchildren. She has 5 grandchildren whom she has not met. Whilst she was living in the UK she worked and we are unsure if she’s entitled to pension at all.

We are in possession of my partner’s parents’ expired Nigerian passports which are endorsed with ILR stamps and letters from the Home Office dated May 1978 informing them that they’ve been granted ILR.

I would welcome any advice that I can be given in this matter.

Thanks in advance.

On current regulations the answer is likely to be "no" - after 2 years absence ILR expires.
And it's unlikely it could be re-surrected after all these years.
You mentioned pension - if her employers deducted NI contributions from her salary there may be a pension entitlement, however I understand it needs 10 years worth of contributen to even get the most basic pension. A pension however would not help her with immigration.
Others will comment to explain the options, if any.

Have a look at the Returning Residents caseworker guidance.

Factors that would be looked at would be the length of the original residence in the UK, the length of the absence and reasons for the absence. However, a lot of weightage seems also to be given to ties (family, personal and business) with the UK. Can the British citizen children demonstrate that she is in regular contact with them? That may help. Also see the examples at the end of the guidance.

I think that the main disadvantage she will have is that her original residence was far too paltry to establish any meaningful connection with the UK. The successful examples given in the guidance seem to show a significant (22 or 32 years) of initial residence, while the first example with 11 years of original residence in the UK leads to a refusal. Indeed, the first example seems to be the closest to your partner's parent, with both the example and your partner's parent having a short period of original residence and British citizen children born in the UK.

I concur with @alterhase58's observation about her not being eligible for state pension. If it is a private pension, there may be specific requirements for a minimum period of contributions before any pension is payable.

Thanks all, I also didn’t think there would be much hope due to the very long absence.