Have a serious think about it. Remind yourself of why you chose this career path initially and the struggles (I assume) you went through to obtain a pupillage.
And if you decide this definitely is not for you and you definitely want to do something else, I would recommend making a 5 year plan and outlining the steps you will take to achieve what you want.
If I were in your shoes I would NOT leave a pupillage to go out into the uncertain. The only conditions I would leave on would be - future job (maybe educational) security. Like a previous poster said, having this on your CV will open many doors for you anyway - some people, after pupillage, decide to work in other areas of law.
The ball really is in your court (haha) on this one. Just please, make a well informed decision. Don’t throw away the opportunity of a lifetime for a a lifetime of uncertainty.
(I have taken into account what you’ve said about this taking a toll on your wellbeing, and I do believe that training for a good deal of professions is going to be this way. If you have the credentials to be accepted for a pupillage, I’m sure you will be able to get into very good jobs, but I’m also afraid that the training will be just as strenuous (unless you have a particular area in mind that you are very passionate about - in which case, perhaps you will enjoy being there more which will compensate for the workload).
Best wishes to you and keep me updated.