What do native Spanish speakers do if they cannot roll the r?

Question

What do native speakers of Spanish do when for some reason or another, they cannot roll their r´s? I´ve seen that many speakers in South America make a zh sound like in the English word measure (I know that with most in South America it is a matter of dialect rather than speech problem, but I´ve met some who have the problem too). Is it the same for native speakers in Spain who can´t roll their rs/pronounce the alveolar trill correctly? Gracias.