#mild speculation

What if Asriel didn’t become a flower again after Frisk left him? What if he waited there by the flower patch where Frisk fell down, dreading the feeling of his love, mercy, and compassion ebbing away as his body changed form once more...and nothing happened? 

What if he looked internally and found not only his own love and compassion, but a little bit from every monster in the underground, a parting forgiveness for his misguided actions? Small fragments of identity and memory from all of his fellow monsters, stuck together and beating in his chest where his own SOUL once did? 

And what if that patchwork SOUL allowed him to remain himself, to retain the capacity for goodness inherent to all monsters, instead of fading into the empty limbo he’d lived within for so long? 

Because to hold the SOUL of every monster within oneself would be the equivalent of holding a human SOUL. And human SOULs, unlike (most) monster SOULs, have an immense power. The will to keep living, the resolve to change fate. 

Determination. 

And although Asriel didn’t remain the God of Hyperdeath for long, perhaps he held that power for just long enough to, with his equivalent human SOUL, create a little determination of his own. And perhaps that determination mingled with the SOULs of all the monsters long enough to form imprints of each - faint, but enough for them all to bleed together like ink through paper. 

And perhaps, when Asriel returned to his boyish form, and the determination faded harmlessly and the monsters’ SOULs returned to their bodies, those imprints continued to sustain his form and existence, allowing him to live with his own sense of self as well as tiny bits of everyone else.