Missy, I'm not sure that I understand your question. If you're asking if Elvis' popularity would have continued without the '68 Special, I do not know because the Special lead to Las Vegas.
Had he just gone straight to Las Vegas without the '68 Special, I think he would have drawn the same reaction that he did when he arrived in 1969. But its difficult to say whether or not he would have begun performing without the catalyst of the '68 Special.
If you are asking if Elvis would have maintained his popularity with the '68 Special without going on to perform live, I think he would have secured his place in history, but I doubt he would have enjoyed the success that he did in the 70's had he just continued with the same thing from the 60's.