sorry for your loss
when did he die? and when was he born (exact dates please).
if he was older than 70.5 in 2019, then yes, he was required to take RMD. if he died in 2020, the rules changed and it may have a different impact.
yes, his 2019 tax return must be prepared and sent it; his passing doesn't change anything
here is what I would do, and it's like being a forensic accountant. Find his 2018 tax return and hopefully the supporting documents (IRA, 401k, etc) are with the return. Contact each company and ask for the 2019 documents so that you can prepare his 2019 tax return.
If you determine he did not take any required RMD's in 2019, get with that company and take it asap. Then you can ask for a waiver from the IRS for the 50% penalty and the reason for the waiver is your father's ill health / passing in 2019. The 2020 RMD is based on the age of the beneficiary and it is still eligible for the 'stretch' provision. If you dad died in 2020, the rules changed. who was listed as the beneficiary on the 401k / IRA - spouse, children, others, estate? the RMD going forward is dependent on that response.
I've made a lot of assumptions here, so let me know if this gets you going in the right direction,.
