That can get long and tiring if you aren't flying!
There are direct trains but no direct flights for this journey. Mumbai (Maharashtra) to Rishikesh (Uttarakhand) distance is 1659 km and you can get there by flight + train in just over 8 hours and 17 minutes or by train fares starting from ₹ 536.
The weather is great for a daytime picnic or game of cricket.