How likely is an offer to be withdrawn after the employer says the offer is being processed but is awaiting internal sign-off?

How likely is an offer to be withdrawn after the employer says the offer is being processed but is awaiting internal sign-off? I recently received a verbal/email offer for a role at a large international company. The HR lady has: told me I was being offered the role; thanked me for confirming my acceptance; asked me for my earliest possible start date because I would need to relocate; triggered an automated Workday email saying “Offer process initiated.” However, I still have not received the formal offer document. When I asked about this, the recruiter replied: “The offer documents are still pending completion of the internal stakeholder sign-off process and will be shared with you once that is complete.” The original vacancy is now closed/no longer accepting applications. My assumption was that headcount and budget would normally have been approved before the company advertised and interviewed for the position. What exactly is usually being “signed off” at this late stage? Does this normally mean they are simply approving the specific candidate’s salary/start date/contract details, or can it mean the company is still deciding whether it has approval to make the hire at all? At this point, would it be reasonable to regard withdrawal of the offer as relatively unlikely, while still avoiding major relocation costs until I receive the written contract? edit: 3 interview, final interview was with my future coworkers, 2 people from my team, the one beforehand was with my line manager and a teammate edit 2: am based in the uk edit 3: the hr lady is not a recruiter, she works for the company and managed the whole employment process