Taxpayer died after filing for an extension to file a 1040 for 2018

The taxpayer filed for a 1040 extension before April 15, 2019, understood to extend the filing deadline to October 15, 2019.
The taxpayer died.
How do I know if I have a personal obligation to file the taxpayer's return?
If so, do I have to file it on or before October 15, 2019? Or does some other date apply? (The taxpayer is a relative, but it may become difficult for me as an unpaid individual to gather all the paperwork for the return.)