You can leave the Schengen area on the very last day of your visa's validity period but it is your responsibility to actually leave no later than the 19th and not to stay longer than 85 days.
If you have got a visa valid until the 19th, it's presumably because you originally submitted a plan to stay 70-80 days starting on the 10th of January. The week or so at the end is a buffer to give you a bit of leeway if something goes wrong (say you miss your plane, the flight is cancelled, etc.)
But if you chose to use this buffer for something else and a problem comes up, it's on you. You will have broken the conditions of your visa and will be treated accordingly.
Do take into account the fact that any transit within the Schengen area also counts as part of your stay. So if your flight to India includes an overnight transit in Copenhagen or Frankfurt, you would actually be leaving the area on the 20th, even if you left Finland itself on the 19th.