You take your chances.
On my Contour SVT.. The front started going bad at 48,000 mi I drove it a year plus before replacing them. That was over 6,000 miles. Then again at 102,000 mi they started to get noisy.
So I drove it for 6,000mi more, then sold it and the new owners have never replaced them either.. So now it is 10,000 miles on noisy front wheel bearings.. On a 200hp FWD car.
This is two years of loud grinding from both fronts. (it was really getting annoying to me with all the noise when i sold it..)
Your mileage may vary.
And ALL mechanics use the 'it will break and leave you stranded" quip.
Naturally they want to make money.
Of anything on a car.. wheel bearings are not gonna strand you.If they start really screeching loudly. THEN worry. just rumbling.. not a problem.
Like the Check engine light. On my Contour SVT I swear the light was on a total of eight full years I owned the car! Out of 13 years bought new until sold it.
One year I got it to go off long enough to just drive to the alternate year inspection, pass, and drive a block and it was back on. I whooped and hollered at that one it was so funny!
Naturally you have to decide what is best for you.
If you like to worry a lot, then get them all fixed. If you are laid back and can accept chance, the just let them ride.
Not gonna make a difference except to your bank account.
If you plan on keeping the car ten more years too. If not.??