וַיַּ֤רְא יִשְׂרָאֵל֙ אֶת־מִצְרַ֔יִם מֵ֖ת עַל־שְׂפַ֥ת הַיָּֽם The Mitzrim died in the Sea, so what does it mean עַל־שְׂפַ֥ת הַיָּֽם?
There was a contingent of Jews who had a hava amina of turning back to Egypt when they saw Pharoah's army pursuing after them. They probably rationalized to themselves, "We got through 210 years of this -- what's a few more years or decades?"
The thing is, once you taste freedom, the spell of oppression is broken and there's no going back. It's like, l'mashal, Adam after the cheit. Once there was a recognition of tov v'ra, whatever that means, you can't put the genie back in the bottle so easily.
So maybe from a distance, the rationalizations held. Maybe from a distance, some could think that, "Hey, maybe things in Egypt were not so bad..." When you face a lifetime of oppression day in and day out, you become used to it, inured to the injustices and violence, and it begins to seem almost normal.
But now, when the Egyptian army drew close, when they stood עַל־שְׂפַ֥ת הַיָּֽם right next to Bn"Y, and the people could look into the eyes of their former oppressors, do you know what they saw? וַיַּ֤רְא יִשְׂרָאֵל֙ אֶת־מִצְרַ֔יִם מֵ֖ת עַל־שְׂפַ֥ת הַיָּֽם They saw walking dead. They saw והמתים אינם יודעים מאומה, אלו רשעים שבחייהם קרויים מתים (Brachos 18). Thanks to their small taste of freedom, the people now recognized their former captors for the brutal monsters that they were.
The physical death of the Mitzrim was perhaps anticlimactic, as it was at this moment that the illusion of Egypt as a mighty empire, as an advanced culture, as someplace Jews had called home for better or worse for centuries, crumbled and died. The stark reality that revealed itself to Bn"Y was that this was no sophisticated empire -- it was a bunch of thugs bent on never surrendering their power. There could be no return to such a place.
This recognition was the precursor and perhaps the precondition to the yam splitting.
(The classical meforshim all discuss the question of what עַל־שְׂפַ֥ת הַיָּֽם means here. The Sanz Klausenberger (Shefa Chaim) has a number of pieces where he explains it similarly to this.)
What an appropriate way to end chag ha'geulah. Hashem is waiting to do miracles for us, but it has to start with וַיַּ֤רְא יִשְׂרָאֵל֙ אֶת־מִצְרַ֔יִם מֵ֖ת עַל־שְׂפַ֥ת הַיָּֽם , recognizing where we are as a dead end. You can't move forward until the illusion that there is something to turn back to, the illusion of security and prosperity in galus, the illusion that this is a safe culture to raise our children in and have a life in, is broken.