Final Accounting in Probate Court

In a probate case in Massachusetts, are the Pension Plan - 401K part of the probate process. Do you have to list it under the inventory even if the funds were paid directly to the only family member? Does it get taxed both on the individual's tax returns and on the estate tax returns and if so, which is cheaper tax wise, to file under the probate or individual taxes? There are no other estate assets.
Thank you,
Denise

Do you mean that the 401k had a named beneficiary and that it has been/will be paid directly to that beneficiary?

That would be a non-probate asset. If that truly is the only asset, why bothering opening probate?

Thank you for responding. A probate was filed as the deceased was murdered by her husband and we needed to open the probate while the 401K monies was fought through the court system. The husband lost the case. So I gather we can just file the final accounting with zero assets and have it closed??