If you are a big company with a few hundred employees and the projects you work on require a lot of team work then leasing office space in Austin might make sense. Some employees could work remote however others may be more productive when working alongside coworkers with which they can collaborate.
Some companies might be better off having all their employees work remotely. Examples might be sales people who travel over 50% or programmers who write code all day and only have to check in a few times a week. Also, If you sell a lot of your products online and everything ships to order directly from somewhere else then having a brick n mortar business may not make sense.
Advances in technology have made it possible for most people to work remotely however still be able to collaborate on projects. Voice over IP, video conferencing, email, text, cloud computing, just to name a few. I don’t think office space in Austin will go away however as technology continues to advance a lot of companies will need less and less of it.