At time $t=0$, swap has zero cost. In fact, both parties may have valued the swap differently based on their zero swap curve-but somehow they agreed. Once a swap is agreed upon it cannot be dissolved because it is an OTC contract.
Even if the first floating payment is known after the first reset, surely the floating payments after that are not known. It seems that one would need to estimate the evolution of the forward rates in time. No book talks about that.
They just assume that the forward rates will be realized; post a ficticious payment at the end; make them look like bonds; find discount rate that matches the value of both the legs. No simulation. I must be missing something here. I will appreciate an explanation.