function makeAlwaysResolve(promise) {
  return new Promise(function(resolve, reject) {
    promise().then(function(res) {
      resolve(res);
    }, function(err) {
      resolve(null);
    });
  });
}

findA().then((resA) => {
  const promiseArr = [findB(resA), findC(resA)];

  Promise.all(promiseArr.map(makeAlwaysResolve))
    .then((responses) => {
      if (responses.every( response => response === null ) {
        res.send(resA);
      } else {
        res.send()// first non-null response i guess?)
      }
    });
})