Usually there are only one or two exit roads, so it's easy to get blocked (especially with emergency services coming in, falling trees, people leaving at the last minute because they ignored the repeated warnings etc.). If I recall correctly, there were quite a number of people who died in their vehicles in the https://en.wikipedia.org/wiki/Black_Saturday_bushfires (see also https://en.wikipedia.org/wiki/2019%E2%80%9320_Australian_bus... -> https://en.wikipedia.org/wiki/File:Bells_Line_of_Road_Bushfi... the road in that photo is one of two main roads through the mountains, when that's blocked, traffic all over the place is affected).

As for internet, assume it's going to go down quickly, if you had any initially (I'd be surprised if a battery powered radio tuned to the ABC wasn't on the list).