Since he is dead, he will not care if the series goes on. His wishes stopped carrying any weight when he stopped breathing.
The part that irks me is that the rights persist with his heirs. Too many people are getting by on the success of their ancestors.
If you are a musician, artist or author and you die, then you are not longer contributing to society. Your family needs to succeed or fail on their own ability and merits.
I can see a case for some rights to persist for a short term. Under the current system those rights are blown out of proportion to their relative contributions to society. Give the family 2-5 years to capitalize on the death of the rights holder, then put it in the public domain. Allow their contributions to society to really be a contribution and not a measure of greed.
As to whether or not a series should be continued against the 'dead' authors wishes, the market will show the viability of the product/work. If no one buys it then it speaks for itself. If it is popular, then it reinforces the reality that the original authors are not the only source of good ideas on that theme.
Some authors actually seem to understand this... They open their 'Story Universes' up to other authors to explore.
You can disagree if you like... That's what makes this system work... The 'right' to agree or disagree.