Editing for clarity.
If by decommission you mean "stop paying the support fees, but keep the software running",
Assuming what you intend to do is to continue using the software but stop paying the support & maintenance fee, that's exactly what will happen. Your current version will continue running, and everything will work as is, but:
I am oversimplifying... but here's what applies to Tridion.
Basic Tridion (since 1999) is a decoupled CMS (Content Management and Website/Delivery are separate applications that can run completely isolated from each other)
Headless CMS is one where the Delivery of content for a website is done over webservices and there is no "CMS logic" inside ...
Try to clarify to understand.
For example Binary Multimedia component A used in Content schema Component B in version 1 later that component updated to changed to use a different image then it becomes version 2. In this case, Binary Multimedia component A still used in Content schema Component B as an Only old version of 1.
In this case, you can go to ...
Once SDL contract is over, what happens to the current running site in
production? Will that stop working?
Yes (if the question tags are correct). But, even if it continues running, having it that way would be using unlicensed software which has legal implications. Contact SDL (RWS) directly to see what your options are.
See also Nuno's comment below. ...
Yes, as Nuno mentioned in his comment, Core Service can be used. And if you ask me, I'll probably use it. Another option, if you plan on just clicking is using Content Porter.
It can export all items with their references, and you can import them into another Tridion Environment. You can also check the packages it creates. They are self-explanatory with a ...
All the content is in the database. Backup your database, there's your backup.
As for migration, good luck. Blueprinting and content relationships will probably make your life miserable while writing the scripts. CoreService is your friend, I guess.
FYI - And this applies to all migrations. If your content structure is wrong to start with, it will be wrong ...
Your Regex looks overly complex, but does seems to work fine on plain XHTML.
However, if you're using DD4T, the XHTML will be embedded in JSON. As a result, the double quotes will be escaped (preceded by a backslash), in which case the Regex no longer works.
Just obtain the DD4T JSON and test it using an online Regex tester, for example: http://regexstorm....
Rich Text styles can be configured in the CMS.
To do this you must
edit the FormatAreaStyles.css to add the styles you want.
Update the SDL version number.
Restart the Tridion CMS services.
Flush Browser Cache.
Then select the underlined text.
You can then select your styles from the Ribbon | Styles.