Two German occupational pension arrangements after an acquisition: keep both or merge?

We are a mid-sized German machinery group, about 4,100 employees, and bought a competitor with 800 staff last year. We run a contribution-based direct insurance arrangement with an employer contribution of 3% of salary. They have an older direct pension promise on the balance sheet, final-pay linked, closed to new entrants since 2015 but still accruing for around 350 people.

Finance would like the liability gone. The works council on their side has made clear that any change to accrued or future rights will be contested.

Has anyone merged or bought out a legacy promise like this in Germany in the last few years? I am trying to understand realistic options and timescales before we engage advisers.