Is it permissible to use a dry material (istijmar) instead of water (istinjak) after urinating, when there are involuntary drops of urine, given that the area dries after a while? And is it permissible to adopt the Maliki view regarding the purity of a small amount of urine?

Using tissues instead of water for istinja' (cleaning oneself after relieving oneself) is sufficient, provided that the area is wiped three cleansing wipes according to the Shafi'is and Hanbalis, or until cleanliness is achieved without specifying a number according to the Malikis and Hanafis. If you doubt that a drop has fallen, disregard the doubt. However, if you are certain that it has fallen and you have wiped it with a tissue, this is sufficient for istinja', though washing with water is preferable. The well-known view of the Maliki school does not pardon even a small amount of urine.