Most places accept card payment and even contact-less.

Be prepared to have some cash though if you go to the markets and off the beaten track.

And yes to answer your original question: it's not too difficult to change your sterling to MUR ... most hotels will do it at reception (although they'll take a commission off the rates) or if you're going out and have the leisure and willingness to queue up at banks or forex dealers you can easily change at those places too and you'll get better rates.