EU 805/2011 Articles 9 & 10 cover licence and rating validity.
Articles 11 & 12 cover rating and unit endorsements and validity of same.
A unit endorsement is only valid if checked every 12 months.
If you fail to exercise a rating during a 4 year period then it becomes invalid.
Each Unit will have a Unit training plan to cover this eventuality.
Does the risk of being unemployed for some time really exist?
Yes.
Unless there is a requirement for your rating mix when you seek a position then your chances can be slim.