I suspect you are asking for guidance about a decision you have made already. Your choice depends on how much money you want to spend on resolving the issue of a dead battery.
Apple gives an estimate here of US$89 to fit a new battery (outside an AppleCare+ plan). This has to be compared with the cost of buying a new iPhone either outright or on a plan from a carrier which would be many time more than $89.
Also, the iPhone 12 series is still fairly young so all other things considered your iPhone will have a few years of life left in it and be capable of upgrading to future versions of iOS for several years, milk spills permitting.
But there is another consideration too, and that is the degree of unseen damage your iPhone might have sustained with the liquid spill and this should be checked at an Apple Store. I doubt they will fit a new battery in an iPhone which has been compromised by liquid. If you are thinking in this direction then it should be taken for inspection.
Otherwise, I commend your choice of chocolate milk. It's my favourite flavour too, but best kept away from technology.