Do you mean would "saving for your retirement" be needed? Or were you specifically asking about pensions?
In any case I don't think any basic income plan works if you imagine that everyone stops saving their earnings and relies on the basic income for their working years and retirement. It is called universal basic income after all and not universal "luxurious" income.
Some type of retirement system would be needed (whether pension, 401K, IRA, or simply "money you saved and invested"). I did some back of envelope calculations that suggest to me that UBI for Americans would be no more than $650/mo - 0 Realistically, it might be $600/adult and $200/minor 5-18 or something like that. Basic indeed.
In that type of a world, people who chose to work during what we today call "working years" would likely feel the need to put some money aside for their "post-working years" so they didn't slip back to the $1200/mo as a couple standard of living.
