Mixed conditional

[impeccableman]

If Darren hadn't wasted his Christmas bonus gambling in Las Vegas, he would go to Mexico with us next month.
(But Darren wasted his Christmas bonus gambling in Las Vegas and he won't go to Mexico with us next month.) adapted from
http://www.englishpage.com/conditional/mixedconditional.html

If Darren hadn't wasted his Christmas bonus gambling in Las Vegas, he would have gone to Mexico with us next month.

Is there any difference between the above two sentences?
Why we can use " would go " instead of " would have gone"?

[Lucretia]

Hello impeccableman,

IMHO would have gone is wrong, because it can only refer to the past while the trip is still in the future.

If Darren hadn't wasted his Christmas bonus gambling in Las Vegas, he would have gone to Mexico with us the following month.
In this case it's OK, because it is sort of future in the past.

[Rusty]

If Darren hadn't wasted his Christmas bonus gambling in Las Vegas, he would go to Mexico with us next month.
(But Darren wasted his Christmas bonus gambling in Las Vegas and he won't go to Mexico with us next month.) adapted from
http://www.englishpage.com/conditional/mixedconditional.html

If Darren hadn't wasted his Christmas bonus gambling in Las Vegas, he would have gone to Mexico with us next month.

Is there any difference between the above two sentences?
Why we can use " would go " instead of " would have gone"?

1) If Darren hadn't wasted his Christmas bonus gambling in Las Vegas, he would go to Mexico with us next month.

2) If Darren hadn't wasted his Christmas bonus gambling in Las Vegas, he would have gone to Mexico with us next month.

1) is an example of a mixed conditional: past and present.
If Darren hadn't wasted his money in the past he would now be able to go with us.
2) is an example of a past unreal condition.
The form is:
If ... Past Perfect ..., ... would have + past participle ... ]
From http://www.englishpage.com/conditional/pastconditional.html "The Past Unreal Conditional is used to talk about imaginary situations in the past. You can describe what you would have done differently or how something could have happened differently if circumstances had been different."