On the warranty extension, I don't know the official policy, but I am aware of a couple instances where a PC was bricked outside the warranty, and Dell offered to fix it under warranty provided the customer purchased a warranty extension. Again, I don't know the officially policy, only what has happened. Just try being upfront with the sales / warranty extension team and seeing if that is an option they will work with you on. That being said, I'd still try the CMOS reset. It is the standard procedure after a failed BIOS update to first try fixing the PC.
I've been loyal to the Dell brand since 2003. An "Urgent" Bios update (from the Dell Support site) bricked by Area-51 R5 that is just 20 months old (1 year warranty expired August 23, 2019). It took me calling Dell 5 times (184 minutes of call time) during a 10 day span to finally speak with a service tech that could troubleshoot the problem. He was professional, polite, and really wanted to be helpful. But, the suggestion was to buy a new motherboard from Dell, the same Dell that flagged my computer for an "URGENT" update, for $600 plus tech labor for installation.  In the end, I was given another number to call to plead my case. Disappointing to say the least. Anyone else have a similar problem that can help before I cut ties with Dell?
Area-51 R5, URGENT BIOS update bricked motherboard