Yes you can travel in case of heavy snowfall they sometimes rarely stop the trek of triund. You can witness snowfall and chills keep extra warm clothes. Yes you can visit dalhousie but it will take whole day trip so keep extra days for Dalhousie. I written 2 articles related to Mcleod Ganj maybe they are helpful to you.
It's not the best time to visit Triund but who cares, travel is not about what's best or not, it's about adventure. But be fully packed because there will be snow for sure at that time. And yes you can visit Dalhousie also but make sure you have 2 more days for this so that you can also visit Khajjiar which is a short drive from Dalhousie. Khajjiar looks like heaven in winters. so don't miss on that.
Hello anjali...we frequently travel to hp in January because of our travel bookings. according to me if u looking for snow and snow fall view then January is a very good month . but Dalhousie gets block if there is extreme snowfall. also dharamkhot gets block if it's heavy snowfall. also if u going solo trip then do all your booking prior to your trip . himachal is safe but still try to do all your booking like car , hotels etc before u start your journey to himachal. also January is considered to be the most freezing month so try to carry your winter stuff.