There's a procedure in the sticky of this forum and if followed deal pending ads will disappear from the TPC mainpage and from open ad searches as these such ads would then be in closed state.
This process isn't mandatory, but if more were using it, this would really help cut down on the number of open ads which which have deals pending that sometimes unnecessarily take up mainpage real estate. Some like to write "deal pending" in the comments and leave the ad open until a deal is complete, but given how easy it is to relist a closed ad if a deal was to go sour, it's really not necessary to have a deal pending remain open.
If there's an ad that has disappeared and one was curious as to if it sold or not, in the TPC search there is an option to search closed ads.
Hope this helps.