Iceman I would stop worrying about them. You have done everything on your end to let them know that they have been missed. The ball is in their court and if they want to they know how to contact you.
My sensei used to worry a lot about people who left suddenly. Sometimes in his after-training talks he would tell us about students who left and what their reasons were. One particularly talented kid was almost a prodigy he was that good, went up through belt ranks quickly and was almost a brown belt in four months; he decided to quit one day because (according to his mom) karate was so easy for him that he was bored with it!(the lesson: talented people often fail to achieve in life because they don't appreciate the things that come too easily to them).
Other families have pulled their kids out of karate for financial reasons, or because of personality conflicts between the kids or even between the parents (which IMO is the lamest possible excuse). Sometimes it is because the kids get discouraged by how hard it is and their parents don't insist that they give it all they've got to reach their goals (becoming more and more epidemic). Sometimes it's the parents who think their kids should be advancing faster and they go looking for another school that will allow their kids to advance guaranteed with each belt test (sensei's response to that: I'm not a prostitute).
Notice that none of the above reasons are within the control of you, the teacher! (and you're obviously not a prostitute)
So my advice is to print out a copy of the Serenity Prayer and post it where you will be constantly reminded that some things must be given up to God.
Blessings to you
My sensei used to worry a lot about people who left suddenly. Sometimes in his after-training talks he would tell us about students who left and what their reasons were. One particularly talented kid was almost a prodigy he was that good, went up through belt ranks quickly and was almost a brown belt in four months; he decided to quit one day because (according to his mom) karate was so easy for him that he was bored with it!(the lesson: talented people often fail to achieve in life because they don't appreciate the things that come too easily to them).
Other families have pulled their kids out of karate for financial reasons, or because of personality conflicts between the kids or even between the parents (which IMO is the lamest possible excuse). Sometimes it is because the kids get discouraged by how hard it is and their parents don't insist that they give it all they've got to reach their goals (becoming more and more epidemic). Sometimes it's the parents who think their kids should be advancing faster and they go looking for another school that will allow their kids to advance guaranteed with each belt test (sensei's response to that: I'm not a prostitute).
Notice that none of the above reasons are within the control of you, the teacher! (and you're obviously not a prostitute)
So my advice is to print out a copy of the Serenity Prayer and post it where you will be constantly reminded that some things must be given up to God.
Blessings to you