Hi,
I am the queen of absess piggies. Waiting for them to pop if not the best idea, but it depends very much on excatly where the absess is and how loose it is. if its close to the piggies jaw lancing is probably to better option allowing it to be opened and dry out.
Surgical removal provides the best success and prevents re-occurence removing it like a tumour and Lancing is the next best thing but it requires a lot of after care.
Waiting for it to burst is not great- Ive been told to leave it before and its grown remarkably overnight and burst. This took months to clear, my piggie was on so much antibiotics he didnt eat for who knows how many weeks. I had to clean the area every day and flush it with salt water twice a day. It stunk to the high heavens and for weeks for and more puss came out as the antibiotics were obviously not reaching the right place to kill the infection. He was a dull very depressed unhappy piggie- please go back to the vet and get a second opinion.