My DD (now 12 months) got better dramatically after starting solids around 6 months. Maybe it's just getting used to having other things in the mouth like spoons, different food textures etc. And if all else fails, someone can always spoon feed her water or milk.
I had a non-avoidable work event when she was 4 months and left her for 4-5 hours. She refused to drink during this time and was tired and hungry when I came back but otherwise fine. I think babies are more resilient than people think. My mum had to cold-turkey me from breastfeeding when she went back to work and I famously refused to drink for 8 hours the entire first day she was gone. Then I quickly cracked the second day and started drinking from a bottle. Survived to tell the tale.
Before DD started solids, I unsuccessfully tried all the MN suggestions - Doidy cup, Baby cup, Miracle Cup, Avent, Comotomo, NUK, Mam, Lansinoh, different temperatures, different nipple flow strength, expressed milk, powder formula milk, pre-made formula milk. It was really expensive and I kept hoping the next one would be the magic bullet. In the end, she just suddenly decided to drink from a bottle and the brand made no difference. We went back to using the very first Avent bottles that I bought during pregnancy.