it's been 10 years or Ten years have passed

[gamboler]

Consider this sentence:

Katherine would have changed a lot. Ten years have passed.
Is it better to say "​Katherine would have changed a lot. It's been ten years"?

Are both correct and idiomatic?

 

[Tarheel]

They both work for me.

 

[tzfujimino]

May I ask a question here?

Would it be wrong to change 'would' to 'will' in that sentence?

 

[GoesStation]

May I ask a question here?

Would it be wrong to change 'would' to 'will' in that sentence?

Not if the context makes it clear that you or your interlocutor are going to see her soon.