Advice needed: take a gamble on Masters offer deferral?

Hey everybody I’m in need of some serious advice. I received an offer for a postgrad course earlier this year to start this September 2024 and was ready to take it up. I’ve actually accepted the offer but the deadline to pay the deposit is coming up next Monday.
For the past year I’ve been working as an intern at a really cool job that I enjoy with a great team. I wasn’t expecting them to offer me an actual job afterwards so I didn’t really consider the prospect of staying. However now my manager is going on maternity leave later this year and she hinted at the prospect of me taking her role over while she’s gone should I decide not to go to grad school this year. This is an extremely attractive prospect to me and I feel it would be ideal as the role is in the field I would like to work in with ALOT of networking opportunities as well as the idea of saving up extra money to be comfortably able to afford my Masters the following year. So I am thinking of deferring my Masters offer.
The thing is I haven’t yet confirmed with my workplace if I’ll actually be able to take this role and with the University deposit deadline coming up I feel I am in a super tricky position. So, should I just bite the bullet and pay the deposit and ask to defer later if this job is really confirmed? The reason for doing this would be so that I’m not left with no masters or no job if i decide to defer without confirmation of this job.
The main problem is I don’t know for sure if my deferral will be accepted and I could possibly be putting a serious amount of cash down the drain if it isn’t. I’d really appreciate some advice.