Well, if that nightmare scenario came true, I’d tell him or her to realize that nothing in life has any real objective meaning
Arguable.
There actually is no objective truth or meaning to anything. No philosopher worth his weight would tell you otherwise. Meaning is what we attribute to things, not something that things have and we discover.
I said “arguable” because it’s dependent on what you want to use the term “objective” for. Just because life has no real “objective meaning” does not mean it also doesn’t have meaning in a specific sense. There are things that make me happy - those have meaning to me.
and no one really has your best interests at heart
Untrue.
Sometimes it is, man.
Sometimes, of course. “No one really has your best interests at heart” is a blanket, untrue statement however.
and that you should pursue only what you find interesting or exciting and not waste a second of your life doing what society claims is good for you or attempting to live based on what other people want or think.
Possibly true, but you have to be prepared to accept the consequences of doing so.
What consequences?
Less money, potentially, for one. Worse health, potentially, for another.