As to the guardsmen:
"A knight of the Kingsguard stood beneath the arch of the door with five Lannister guardsmen arrayed behind him."
"Five men were down, dead, or dying by the time Arya reached the back door that opened on the kitchen."
I suppose the chances are same on Syrio being dead, and alive. As there is nothing in the book concerning his fate, I guess we will either find out in later books, or never know.
Also, I believe, that the metallic clang in the TV show was coming from the fighting upstairs, even though she turned around. At least it should, if it was to be according to the book. Arya ran through the kitchen first, just then she got to the stairs and I believe that no sound from Syrio should have been able to reach her by then.
That is the same feeling I got because in the book it doesn't say she heard the sound of a sword hitting the floor...and yes we can say for certain those 5 men were dead, if I recall correctly he started off by dodging and one of the unbalanced guardsmen lurched into the other and they both went down, then he stabbed that guy's eye out, then as the two on the ground were getting up he took one's cap and kicked the other in the face, the one with the dagger then was blocked by the cap and had his knee cap shattered, Syrio then dodged another great wood-chopping swing and it caught the guy with out a helmet right in the collarbone area, then before he could get the sword out of his comrade Syrio smashed in his throat with his stick. Then it says that there were 5 men laying on the ground, dead or dying.
Another point I thought was different in the show was how certain it was Syrio was dead, because as Arya runs away all of the guardsmen are getting up and Ser Meryn had Syrio in close holding on to his arm (I think) and then smashing his wooden sword. I found it even more odd that G.R.M.M. was the one who directed that episode, so I think it might be that Syrio really did die but G.R.M.M. wanted to change how that scene played out so it was more obvious. Having said that, I really do hope Syrio comes back because I need to hear "Just so" a few more times.