Monaware and the bassist conducted a soul-transference in that moment and became two starstruck lovers, who were destined to meet again at some unspecified time in the future
I thought for sure Mario and Princess were gonna get actually-married at the end of Odyssey, but Nintendo would never freaking lock themselves into something like that I guess.
It surely would've made Odyssey more memorable though... "Oh, you mean the one where Mario and Peach got married...