What to Do Now?
If LinkedIn is an important part of your social media tactics not everything is lost. You can still leverage on one-to-one introductions and LinkedIn Ads. The company suggests to use the sharing features, but to heavy Events App users that may come as an insult.
Unfortunately LinkedIn let go a pretty unique service due to the audience it managed to captivate. Therefore finding a real alternative may be difficult. In fact publishing a high profile conference on Facebook or Google+ may make it look like a sweet sixteen party. The cited platforms do not offer a business events solution and are quite focussed on pictures rather than offering proper event marketing tools.