The mRNA is destroyed in the process of its decoding by the cell...
Re: “The mRNA is destroyed in the process of its decoding by the cell...”
Start pedant mode
Just as a point of information: RNA, including mRNA, generally lasts until it’s broken down by specific enzymes. In general, until the RNA is actively broken down, it just sticks to the local ribosomes, guiding those ribosomes to continue making proteins. The mRNA doesn’t wear out by this process any more than a punch card wore out in the control of a an automated loom.
It sorta has to be this way, as mRNA is generally about an order of magnitude physically larger than the protein for which it codes. The reason it’s more efficient to make protein from mRNA rather than to just inject the protein directly is that each individually large mRNA makes many many many copies of the individually small protein, so that the total mass of protein made is much larger than the total mass of mRNA utilized in the process.
End pedant mode