The show takes place in the time that Rick is in a coma, and the two are obviously in the same universe, so it's logical to think that at some point the two shows could feasibly crossover in some way. Smaller characters, such as Dr Edwin Jenner (Noah Emmerich) and Juan Gabriel Pareja's Morales, were rumoured to be making an appearance, but that hasn't come to anything as it stands. However, given the timeframe it's probably not possible for any of the main characters to appear, and those behind the show have said it isn't their intent to catch it up or have it directly crossover. The producers have said, though, that there will be some links between the two - aside from the hoards of zombies all over the place - with some key pieces of information being inserted into the show, with the aim to create an "overall tapestry."