A word for someone/something that is hopeless and 'incurable'

Terminal, Cambridge English Dictionary

(of a disease or illness) leading to death:

His mother has a terminal illness.

By extension, one can use terminal as the OP did, to describe the condition of a company or an institution that cannot survive. Oxford English Dictionary:

c. fig. and in extended use: irreversible, irreparable; extremely severe; calamitous, disastrous.....

1981 Daily Tel. 21 Dec. 2/1 Another contest for Labour's deputy leadership next year could prove ‘terminal’ for the party, Mr Neil Kinnock..said.

....

1996 Big Issue 15 July 12/1 The business went into what many thought was terminal decline.

.....

And, in case a reader cannot access the OED, see this definition from Oxford Dictionaries

2.3 informal [--] Extreme and usually beyond cure or alteration (used for emphasis)

‘an industry in terminal decline’

‘you're making a terminal ass of yourself’

How about irredeemable?

Incapable of being redeemed or bought back.

• Oxford English Dictionary

Hence, redeem, note the original definition first and then the definition that would apply here.

1.a. to deliver (a person, a soul, etc.) from sin or damnation.

2.b. To make good (a loss).

• Oxford English Dictionary

Example uses:

Six months later, the damaging consequences of this fateful choice are undeniable–and I believe irredeemable.

• Forbes, 2009

Think Washington, D.C., and your statehouse are irredeemable and unproductive? Look to city hall for answers.

• Business Insider, 2017

So in your sentence, it would be

Yahoo is irredeemable anyway, no one could save it.