This is depending on the rate of decarboxylation. If 3 rapidly decomposes by decarboxylation, then the amino acid 2 will not be obtained. However, I think this happens under heating. Thus, if you mix the amino acid with ninhydrin at rt, you will have an equilibrium reaction; this can be pushed to the left side by adding excess water. Dehydrating the reaction mixture will push the equilibrium towards product 3. This is just based on the reaction-equation, and not backed up by any experience with the reaction you desire.

3 is an imine (Schiff Base) and, as long as they don't suffer further reactions (like reduction), these compounds are know to suffer hydrolysis. Therefore, it should be possible to recover 1 and 2 from the hydrolysis of 3 in basic aqueous media.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1172855/pdf/biochemj00536-0260.pdf

http://www.znu.ac.ir/data/members/ahmadi_ebrahim/Advanced%20Organic%20Chemistry/Advanced%20Organic%20Chemistry-Problem/%DD%D5%E1%208/27.pdf

http://pubs.acs.org/doi/abs/10.1021/ja00864a031

https://www.jstage.jst.go.jp/article/cl/30/7/30_7_708/_article

Amino acids are colourless organic compounds. When a chromatogram is developed during their chromatographic separation, they give colourless spots. In order to make these spots visible to the naked eye, some locating agents are sprayed over the chromatogram. Ninhydrin is one of the most commonly used locating agents. Detection of amino acids even in very small amount can be accomplished readily by the ninhydrin colour test. Ninhydrin is a cyclic triketone compound. When an alcoholic solution of ninhydrin is heated with an amino acid, it produces an intense violet-blue colour. The sensitivity and consistency of this test is such that a very small amount (in micromoles) of amino acid produces a colour intensity which is reproducible to a few per cent provided that some reducing agent such as stannous halide (SnX2) is present to avoid the oxidation of the coloured compound by the dissolved oxygen.

The reaction is reversible in the presence of acidic solution as ninhydrin forms basic compound in the presence of water.