Lan, I'm in a position similar to hadabeardonce. I worked for a government employer, vested in a small pension, left the job long before draw date, kept the pension instead of rolling my contributions into an IRA.
I calculate that I still get a larger benefit from the pension than I would from investing the contributions. You should explore the details of different options because the details can change the outcome of which option is best.
The high 20% contribution makes me think of one of those government pensions that have high matching. In my case, the employee put in about 6% and the employer put in about 7%. But if the employee withdraws the funds, he/she only gets to keep the 6%, plus a small percentage representing bond-like investment returns over time. In other words, I wouldn't get to withdraw the employer's part of the contribution. Would you get to withdraw the employer's 20%? Or would you lose it by abandoning the pension?
Once you know the answer to questions like these, you can make reasonable calculations to compare the financial value of different options.