How many people do you think the Catholic church loses because they are unable to maintain that vow?
I assume you mean how many priests leave the priesthood for that reason. I don't know. I've never seen any statistics on the matter. A lot of priests left the priesthood in the past 30 or so years, some because they wanted to marry.
I've read a number of articles by some who left and married and who regretted doing so. They regretted the marriage, but moreso leaving the priesthood.
That's kind of like saying "How many people do you think the police force loses because they are unable to uphold the law?"