Renewing student visa (re-enter as visitor)

Hi. I'm currently renewing my student visa and it's still in process. However, I had already booked a trip around Europe countries in another week. If my visa has not done by the time i leave for the Europe trip, is it possible if I just proceed with the trip and re-enter UK as visitor? or can I explain to the immigration officer that my visa is still in process?
Thanks.

Surely you had to send your passport with your renewal application? How will you travel if you don't have a passport?