I dont really think the moss thats inside the mesh will rot and fall apart since java moss is pretty versatile, can be without light for a while and still survive. Though I would still trim it since the more you trim the bushier it will become. Also not sure if the link you provide stated it but, its best to mince the moss into smaller pieces, that way when it grows it will grow fuller right away since there will be more strands producing.
I am growing mine, about a 5x10 section in a 29g, ive clipped it to the top of the tank so it gets the most amount of light, so far so good.