Is this a common behavior from his part or is this a one time incident? Have you and your Master had a clear communication on establishing what to expect when you are apart from each other? If this said incident is completely out of character of him, I would say that you have every reason to be worried. Given the pervasiveness of technologies nowadays, one should be able to find some way to communicate except under very specific circumstance. If this is a common behavior, then I would suggest you bring your concerns up to your Master and hopefully the two of you will find a way to address those concerns for future events. D/S relationship or not, respect should always be mutual.