Does the prayer of one who said the two Tasleems without the intention of Tasleem become invalid, and is all that he prayed rendered void?

The summary of the fatwa is that it is not a condition for the validity of the taslim (salutation) at the end of prayer that it be accompanied by the intention of concluding the prayer. This is the preferred view in the Maliki, Shafi'i, and Hanbali schools of thought, whereas for the Hanafis, taslim is not obligatory at all. As for the intention of greeting those present in the prayer, it is not obligatory, but rather recommended. To avoid disagreement, it is better to intend concluding the prayer and to intend greeting those present with him.