It's tough to say.
The number I hear thrown around as a 'rule of thumb' on most stock motors is a life expectancy of about 1000 hours - well maintained, of course. 700 is getting up there, as is the age.
700 hours on a motor 3 years old verses 700 hours on a motor 14 years old also makes a huge difference. I honestly wouldn't expect them to last much longer before a rebuild is necessary.
But having said that, I know of a guy who owns a commercial boat with a pair of 496's who has turned 2000. However, they're only 2 years old.