Hi everyone. Can someone check those sentences? Are they grammatically correct? There might be some mistakes in them because I took them from online English quizzes. I just want to make sure they are correct.
Thanks a lot!

1. I’d rather I didn’t have to work next weekend, but I do!
2. He saw a therapist for several years after he left school.
3. My father’s not here. He went to his office.
4. The children are not here. They have gone to the cinema.
5. Do you think you will have finished with my mobile phone soon? I need to make a call.
6. You had better start looking for another job pretty soon. I have a feeling that you're going to get fired before long.
7. No matter how rich people are, they always seem anxious to make still more money.
8. Oh, I am really sorry. I wish I have never attempted to lift that vase.
9. If you should happen to be passing, drop in for a chat.
10. They can’t have swum across the river; the currents were much too strong.
11. I don’t think I can meet your deadline. Could I have a few more days to do it in?
12. We’ve got a few DVDs which we haven’t seen if there’s nothing on TV tonight.
13. By the age of 18, I had decided not to go to university.
14. Your diet is terrible. You don’t eat many vegetables.
15. Do you mind if I open the window?
16. You're interested in buying a property, is that right?

Question

Hi everyone. Can someone check those sentences? Are they grammatically correct? There might be some mistakes in them because I took them from online English quizzes. I just want to make sure they are correct.
Thanks a lot!

1. I’d rather I didn’t have to work next weekend, but I do!
2. He saw a therapist for several years after he left school.
3. My father’s not here. He went to his office. 
4. The children are not here. They have gone to the cinema.
5. Do you think you will have finished with my mobile phone soon? I need to make a call.
6. You had better start looking for another job pretty soon. I have a feeling that you're going to get fired before long.
7. No matter how rich people are, they always seem anxious to make still more money.
8. Oh, I am really sorry. I wish I have never attempted to lift that vase.
9. If you should happen to be passing, drop in for a chat.
10. They can’t have swum across the river; the currents were much too strong.
11. I don’t think I can meet your deadline. Could I have a few more days to do it in?
12. We’ve got a few DVDs which we haven’t seen if there’s nothing on TV tonight.
13. By the age of 18, I had decided not to go to university.
14. Your diet is terrible. You don’t eat many vegetables.
15. Do you mind if I open the window?
16. You're interested in buying a property, is that right?

Answer

Only one actual error. A couple that sounded a tiny, tiny bit odd, but nothing wrong with studying them.

8. 'I wish I HAD...'

Answer

Number 9 is not exactly incorrect, but this would be preferred ...
"If you happen to pass by, drop in for a chat."
Or more formally
"If you should happen to pass by, drop in for a chat."

Pass without a direct object can also be used to mean die, as in
"My grandfather passed last year" 
This would be understood to mean "My grandfather died last year" not "My grandfather walked nearby last year."