You can avoid losing items or progress by force-closing the game (Alt+F4 on PC, "Close App" on console) before dying or failing a mission. This resets you back to the safehouse as if the mission never started.
Whenever New York is an option, take it. Robbing the vault provides a massive amount of Mercers and often carries a high XP payout for the objective. hitman 3 exclusive freelancer mastery cheat
Upon reaching Mastery Level 60 and filling your weapon wall, you can use the prestige laptop to reset your inventory for a permanent XP bonus multiplier. You can avoid losing items or progress by