New Shift Supervisor and I’m unsure if I should continue

I got promoted to Shift Supervisor about a month or so ago from crew member after working at my store since August. For a bit it was me, another shift, our AGM and our GM. A couple hours ago the AGM texted me apologizing and saying he’s quitting and will not show up tomorrow for his closing shift. It’s my day off but I’m probably gonna get called to cover his shift, which is noon to 10pm, and I’m not sure what to do because I really want this day off. I close the next 3 days and really don’t want to close 4 days in a row. Additionally, I’m worried that I might get really screwed over with shifts, since we’re short a manager and the other shift supervisor is going to quit in mid-June. I applied to a couple other places preemptively because I’m worried I’m gonna be worked into the ground. Any advice?