My son was named the Executor of my mother's estate ( already probated 3 years) he is receiving a settlement from a wrongful death case. There no outstanding debts for the Estate that needs to be paid, this is strictly his part of the settlement. Does there need to be an Estate account opened or can he just deposit ?
The bank we deal with now ( 8 yrs) will not deposit the check into account without an updated testamentary which again has to go through Probate and will take another 3months or so, and by that time the check will more than likely be VOID from the insurance company. I have asked the lawyers handling the wrongful death suit to make it out to him alone, no Executor, no Trustee, just him name, but I am told it can't be done that way.
What should we do?

Your son should have a document stating that he was executor of the estate. I'm not sure why the bank is requiring an "updated" testamentary. The court clerk should be able to issue a statement that your son was the executor and therefore entitled to deposit checks made out to the estate.

By the way, the estate should NOT have been closed until the wrongful death suit was resolved.

You imply that he has the check in hand, but then say that the lawyers won't write a check to him. Which is it? Who is the check made out to?
If to him as executor as you suggest in your title, it has to go in the estate account. Is that account closed and probate final?

Have you talked to the probate court?
If you need a new check at 90 days, that should be a minor problem. And probate should be able to reopen the case in less than 3 months anyway.

... The bank we deal with now ... will not deposit the check into account without an updated testamentary which again has to go through Probate and will take another 3months or so, and by that time the check will more than likely be VOID from the insurance company. I have asked the lawyers handling the wrongful death suit to make it out to him alone, ... but I am told it can't be done that way. ...

If it is your son's wrongful death settlement, and not an asset of the probate estate, the party with whom you son settled apparently doesn't see it that way. But if the estate has some claim to the settlement, they would be correct.

It appears that there is some disagreement as to whether your son is acting in behalf of the estate or not.

I find it hard to believe that a court would take three months in which to re-issue letters testamentary. But in any event if it does take that long and the check is no longer current, your son can ask the other party (or that party's insurance carrier?) to write a new check.

Settlement checks are not issued without a signed settlement agreement. What does that agreement indicate regarding whether he represents the estate or not?

Also, you have no business asking the lawyers to make it out to him alone. Presumably he is an adult and competent (else wouldn't have been appointed executor in the first place). If he needs help negotiating this, have him see an attorney.