It's possible to get refunds for all Diablo Immortal purchases, but the penalties are so high that you'll want quit playing soon afterwards.
Diablo Immortal players are having success getting full refunds for items and content purchased in the free-to-play game. Blizzard has honored multiple refund requests (here and here) for in-game purchases. But if you're going to ask for a refund you should be really sure you want to stop playing.
Blizzard will indeed refund Eternal Orb purchases for a steep cost. After the refund, players' Eternal Orb balances are put in the negative and you're essentially indebted to Diablo Immortal. Once in the red, the game will significant restrict what you can do. Being in Eternal Orb debt means you can't equip any items, play with others in any sort of multiplayer gametype--you can't team up--and you also cannot break down or recycle items at the blacksmith.
"All purchases have been used in some form. This means that the refunds will withdraw all eternal orbs from those purchases, meaning they go into negative orbs," Blizzard support informed one player who had requested a refund.
"This will prevent you from playing in a party, equipping items and salvaging until you purchase enough orbs again to get out of the negative."
The negative balance is account-wide, and there is no guarantee that you will get a refund if you request it. Gamers are instructed to specifically ask for a refund and go into the negative. Also be sure to not charge back anything because Blizzard will ban your Battle.net account.