Cannot remember which, but one that was said something like ".. and today I have perfected your religion for you...." meaning that the Revelations were finished (Quran 5:3)
You see, because I am a born muslim, many facts and facets I know but when asked specific questions like that, I am not sure of where my source comes from so it is hard to honestly answer without careful research.
But off the cuff, I would use different reasoning, parallel, in tangent so to speak to 'endorse' that statement. These ayahs are in the Quran (not sure where, though) like the one about protecting it from corruption (that is a very tall order unless Divinely ordained) and why would it need to be protected from corruption? Perhaps because there is going to be no more messengers? Previously, the messengers had always another one to follow, to correct and give guidance.
Why was prophet Muhammad brought up in the dessert, away from the town and the people? Why was he illiterate? Perhaps Allah wanted to be his Teacher. Allah alem.
I believe, in all honesty, the Seal of the Prophets, the Final Messenger etc was already known many, many successive generations of previous prophets, peace be upon them all. They would foretell about the future prophets and the one to come. They would be given 'signs' about him, about the hour or whatever that would be used to identify and verify the authenticity of that person. So his arrival (Muhammad pbuh), for those who accepted him, already know they are following the final messenger. For those who do not believe in his authenticity still await their final messenger.... or have the successive generations forgotten about it?
The thing is, for muslims are forewarned! There is no other prophet! The next that will have i-n-c-r-e-d-i-b-l-e- powers to convince the masses that he is the final one, with god's powers, will be Dajjal. He will be followed by those who rejected Muhammad pbuh and are still waiting for their prophet. That is it, simply put.
But for those muslims living at that time, it will be like those times of early Christians in the Roman empire. Maybe worse. Allah alem. Lots will give up faith, apparently.

eace: