You say pension. Do you mean a 401k, or a defined benefit pension? (i.e. one that will pay a certain amount per month at a specific retirement age)
In either case, I would still roll it over to an IRA: the company could change its policies at any time, and since you aren't an employee, you may get late notice because you don't have access to regular company communications. You may miss deadlines for action, or have to make critical decisions in short order.
In the case of a defined-benefit pension, if the pension plan defaulted, you would be put in the gentle hands of the PBGC. Your fate would be out of your control, irrevocably.
So, especially if it's a defined-benefit plan, but really in wither case, roll it over. Then it is fully yours, with the standard selection of low-cost, public index funds. You don't need anything more complicated than that, and you won't have to regularly be in touch with an organization that may bring up thoughts of your ex.