In Stephen King’s It continuity, Will Hanlon (Mike Hanlon’s father) does not die on-screen during the events of It: Welcome to Derry, but his eventual death is known from the wider canon.
Fate in the TV series
In the prequel series It: Welcome to Derry, Will survives Pennywise’s attacks and lives into adulthood, later becoming the father of Mike Hanlon, the future member of the Losers’ Club. The first season ends with the Hanlon family remaining in Derry to help keep watch over Pennywise between cycles, confirming that Will is alive beyond the events shown.
How Will ultimately dies
Outside the prequel’s timeframe, supplementary material and fandom sources based on the original It novel describe Will Hanlon as dying of cancer in 1962. Some modern coverage of the new series also emphasizes that, despite surviving Pennywise, Will’s story is tragic because his eventual death comes from illness rather than the creature.