We have standalone one-shots games as well as drop-in drop-out campaigns which isn’t affected if you cannot attend the following week.
If you are playing in a regular campaign then it is generally expected that you will be there there for most / the majority of weeks. However, exceptions can be made depending on your Game Master (GM) and you should speak to them, or a group organiser, at the earliest opportunity. Some of our members need to travel away every few weeks or work a constantly changing shift pattern: but we have still managed to fit them into campaigns.
And there’s the age old saying that “Real Life Comes First”: we know and understand this, so please speak to a group organiser if you have any problems.