Sometimes an AddOn still works with a new patch, it's just that the version the AddOn tells WoW it is compatible with is lower than the latest patch version. So, if you're adventurous, you can try to just change the version the AddOn reports to match the new patch version and see if it still works.
Warning: These instructions may cause your WoW to crash or freeze or have some other unexpected problem so, be ready to remove the AddOn you're editing out of the Interface\AddOns\ directory, if you start having problems.
I will use QuestHelper as an example...
1. Look for your C:\World of Warcraft\Interface\AddOns\ directory (or the Interface\AddOns\ wherever you installed your WoW program, if a Mac).
2. Find the QuestHelper folder and make a backup of it.
3. Open the original QuestHelper folder and look for QuestHelper.toc file.
4. Open the QuestHelper.toc file in a text editor (Notepad, WordPad, Text Edit, etc.) and look for a line that looks like:
## Interface: 20400
Note: This example stands for patch version 2.4
5. Change the number (20400) to the new patch number (x0yz0; for example 2.4.3 would be 20430) and save the file.
6. Now the scary part. Launch WoW, login and choose a character to play.
7. Make sure your QuestHelper is not turned off in the AddOn control list. It should not appear as out of date.
8. See if QuestHelper still works okay. If not, quit WoW and remove it from the AddOns\ directory.
Anyway, this is usually what I do until an AddOn developer updates an AddOn. Most still work, but some don't.
Also for the record, I don't use QuestHelper because it freezes my WoW, so the steps above are based on how you would do it if you used QuestHelper.