How could the daleks have fought in the last great time war when they were destroyed in remembrance of the daleks and why is there not one episode of the last great time war in dr who?

If you think about it, there have been a lot of Doctor Who episodes in which the daleks seem to be wiped out, but are shown in other episodes as not having been destroyed. Therefore enough Daleks must have survived. Also, in the Doctor Who version of the 22nd Century, after the Dalek wars between the daleks and earth, all the Daleks suddenly dissapeared. They in truth had gone to fight the time war against the Time Lords. They were then almost all destroyed. The reason there are no episodes of Doctor Who set in the time war is that when the show returned Russell T. davies wanted to picture the Doctor as the last survivor of his race, and to keep the events of the Time War a mystery, and give little hints to some of the things hat happened in the Time War.