If Facebook closes down, would you still proceed with developing a social media strategy for your business using other social media platforms?

If Facebook shuts down, there will be definitely an alternative platform to engage with customers.
Choosing the right channel depend on the category of business.
A micro-blogging site can be the perfect place for spreading quick and direct information, Pinterest is an ideal platform to aggregate all visuals by category.
As for sharing some informal content and showing the casual face of the company, Instagram will be the place.While communicating audio visual stories, goes first to Youtube, we can now also make the message shorter and quicker via vine or instagram.

yes ofcourse, facebook brought a standardizes basic social community presentation to the world, so can adopt the basic techniques of the facebook to catch the marketing as well as for the social services.....

Definately & absolutely. In this dynamic global business environment or global village; social media platforms are largely influencing business processes & transactions. Almost everyone can now access social media in one way or the other, there it would be good to develop a social media platform for a business. But before embarking on such a project, you need to do extensive research & know the previous social media platfrom failed abd then you can be to make a good decision

Honestly , Very absurd question. Social media and Social media marketing will always exist with many alternatives.