>>13183285They could go beg SpaceX to procure some Raptors (wouldn't be a drop in replacement but nothing ever is, and since SpaceX would be setting their price they would be in a position to sell each pair of raptors for 1000% of their actual production cost, not like anyone is going to be able to reverse engineer that thing anytime soon).
They could also go beg Aerojet for the ORSC kerolox engine they originally offered ULA.
Alternatively they could really bite the bullet and say fuck it we're developing a brand-new methalox gas generator engine based off the SLI designs from the 90's and we're gonna stretch the Vulcan tanks to accommodate.
Doesn't really matter anyway because even if BE-4 engine development had gone perfectly and Vulcan started launching this year, Starship is going to abort every modern and upcoming launch vehicle anywhere that payload operators have the ability to buy SpaceX services, which means pretty much everywhere except China. We are heading into a decade where Starship is doing 99.99% of everything in a far bigger launch market than our modern one, the remaining 0.01% is sensitive government launch contracts that only exist either in nonfriendly countries or as cope (this is where ULA will cling), and following this decade is when we will start to see serious Starship-competitor vehicles (ie china cloneship, ESA will do something, Roscosmos will release a render but never build anything real and will probably collapse entirely, and maybe some more American space companies will come aroudn to their own Starship-style vehicles).