My item was supposed to arrive nearly 4 days ago, seller hasnt responded!!

I bought something that is super sentimental to me, I really want to have it with me at the hospital for my daughters birth in October. Im desperate to receive it lol. The seller was great & shipped out within 72 hours of my purchase. The tracking information shows that its about 20 miles out from where it was originally dropped off with USPS, it hasnt moved any further since the same day it was shipped. It was supposed to arrive very early Monday morning and we are now going into Friday, Seller hasnt responded to my message asking if they can help me. I raised the issue to depop in hopes they would be able to get the sellers attention on the matter. What is likely to happen? I just want the item, I’ll be devastated if it doesnt ever show up. Is this something that depop will escalate or eventually refund me for? Ive never had this experience before so hoping someone knows how this might play out