Can anyone think of a solution to this knotty problem?

We ship a program as a merge module, used by various OEMs in their products. An end-user may install several different products that include our program. Thanks to Windows Installer, only the latest version of our program will be active.

Until now our product's components have never changed when new file versions are built.  But now, after many years we need to add a component to our program. So there are complications:

Say Product A includes our component X, and Product B includes our component X plus our component Y.

If a user installs both A and B, they have components X and Y. If the user later uninstalls A everything is fine, X and Y are still on disk and B works. 

However, if B is uninstalled first, leaving A in place, then Y will be removed which breaks our program and product A.

One approach might be to use a custom action in the new mergemod to manipulate the SharedDlls reference count for Y, so msiexec doesn't remove it when B is uninstalled:

e.g.  IF refcountX > 1 and refcountY = 1 THEN increment refcountY

This will leave component Y orphaned after A and B are both uninstalled, which isn't very tidy but avoids breaking things. But it only works if A is installed before B.

Is there a better solution?