I've been looking for that operator too! I came up with a solution for my needs that I hope will help yours. It's not the best solution most likely, but I hope it can help until a better solution can be found by some others on here, or until this operator is added back in 5.0 (hopefully!) :)
var Observable = Rx.Observable;
var source1 = Observable.create(function(observer){
observer.error();
});
var source2 = Observable.create(function(observer){
observer.next('Continuing on');
observer.complete();
});
var stream = source1.catch(function(data){
return source2;
});
stream.subscribe(function(data){
console.log(data);
});
JS Bin Example: https://jsbin.com/qadozoveta/edit?html,js,console