Game of Thrones' writing is so bad now...

[Turalyon]

If Cersei wins the war, they would have contracts for years to come and they would only commit IF it was easy. If it isn't, they kill Cersei and walk away. Or, they don't kill her and walk away anyways.

The Golden Company are billed/having a reputation as being the most highly regarded and respected amongst other mercenary groups. Only institutions of great power would be able to hire them anyway. If they ransomed their employers for easy contracts (ie: having benefactors accompany them in all contracts) and "never broke their contracts" (as they are apparently known for - so they'll never just "walk away" anyways) by killing potential benefactors if things going awry in the field, that would give them a more notorious reputation/they wouldn't be so desirable/too demanding.

Cersei is not putting herself at risk in her mind because she assumes an easy victory.

I'm not sure if that was really established. I think Cersei knows the potential threat of the White Walkers (having seen one of the wights) and is unwilling to send her own troops, nor herself, because she would rather have all her enemies die without weakening her own position and/or thinks King's Landing is a more defensible position than moving out against them and exposing herself. It's why a mercenary group is useful and employed instead. Coming from Essos, they probably don't know about the threat of the White Walkers and are just assumed to lay siege to Winterfell - which has fallen about a few times already (Greyjoys, Boltons and then recently the Starks).

[sandwich_bird]

The Golden Company are billed/having a reputation as being the most highly regarded and respected amongst other mercenary groups. Only institutions of great power would be able to hire them anyway. If they ransomed their employers for easy contracts (ie: having benefactors accompany them in all contracts) and "never broke their contracts" (as they are apparently known for - so they'll never just "walk away" anyways) by killing potential benefactors if things going awry in the field, that would give them a more notorious reputation/they wouldn't be so desirable/too demanding.

Lets forget about them killing her. She's broke and wants to hire them to finish off Winterfell. The GC tells her their price is based on the assumption that they'd have a fully defended northmen army to deal with on top of dragons and etc. Cersei can't afford that contract so she proposes an alternative contract that assumes that winterfell will be weak when they arrive. As a show of faith in this assumption, she's willing to walk with them all the way there as a proof. The GC agrees to this contract but if the assumptions of that contract turns out to be false, they don't need to commit anything as the contract would be then essentially void.

I'm not sure if that was really established. I think Cersei knows the potential threat of the White Walkers (having seen one of the wights) and is unwilling to send her own troops, nor herself, because she would rather have all her enemies die without weakening her own position and/or thinks King's Landing is a more defensible position than moving out against them and exposing herself. It's why a mercenary group is useful and employed instead. Coming from Essos, they probably don't know about the threat of the White Walkers and are just assumed to lay siege to Winterfell - which has fallen about a few times already (Greyjoys, Boltons and then recently the Starks).

I agree that she does understand the gravity of the problem but the line "let the monsters kill each others" is an indication that she expects the problem to solve itself. At the very least, it definitely opens the possibility to go write it that way.