Uncashed refund of excess deferral

A participant in a 401k plan deferred more than the 402g limit in 2020. An appropriate refund check was issued timely. But the participant never cashed the check. Now it's past the deadline. If he cashes the check now, is everything ok? If the check goes stale dated and a new one has to be re-issued, can it be done under the original check date? If not, I assume the funds just have to stay in the plan, leading to double taxation on the excess.

Here's some fairly recent discussion that should be helpful: