Bit of an alarmist article title when plenty of fairly popular alternatives exist, like AOKP, AOSB, Slim, and PA. Was CM doing something extra to/with their ROMs and code that these are not?
PA - dead
AOSB - Exceeded bandwidth and archive doesn't seem to have archived it properly. According to Google cache, they're working on L, so seems dead.
Slim - was dead for a few years. Seems to have revived.
The question is what will LineageOS look like?
I thought so too but, based on a quick search I just did, it was relaunched in 2016.
Certain custom ROM's such as ParanoidAndroid [2] used AOSP as a base prior to CyanogenMod getting shutdown so these ROM's would not be impacted.
The nice thing about CyanogenMod was the wide variety of devices they supported. This meant you could get a newer version of Android/CM on what would have been an otherwise unsupported device by the OEM/Wireless Carrier. CyanogenMod was generally the model project for other third-party custom ROM's.
[1] http://source.android.com/source/index.html [2] http://www.paranoidandroid.co/
CM supported more than 500 devices, the only other ROM that is even close to that is MIUI which supports about 200 devices (most of which are in China).
Other ROMs support less than 50 devices. Some even keep it limited to Nexus devices only (read CopperheadOS).
AOKP is based on CM
AOSB isn't being officially updated to even Lollipop I think.
SlimROM is active but yet again quite limited and slow. They released their ROM based on M late this year which is very late in terms of custom ROMs standard (even most OEMs by then had released M for their devices)
Paranoid Android is active but limited to about 30-40 popular devices.
CM was known for supporting devices which the OEMs ignore after 2 years of launching them. And once CM was released for it many other custom ROMs were developed based on it to keep devices updated. This is the main reason why CM is most popular and appreciated for.