Mmm, not seeing any obvious death for an Elizabeth Leitch/Seitch previously Sinclair, however, and it may just be co-incidence and an entirely different chap, but there is an Archibald Leitch marriage in Bengal on 28th June 1843 at Calcutta to a Rosanna Owen.
One transcipt has nothing against age for Archibald, and against status has '26, ship carpenter', whilst another has groom's age 26 and father Archibald Leitch. So, was he aged 26 or was the 26 in reference to something else?
On the Archibald Seitch to Elizabeth Sinclair marriage, one transcript has him as Seith and no age or status recorded, whilst another has nothing against age of Archibald, and against status has 'Pte., H. M. 26th'.
Update: Is it a co-incidence that '26' appears on both records? Could one source have mistakenly transcribed it as an age when it wasn't? Original of the Leith/Owen marriage clearly has an age column and says 26yrs, it also says bachelor, so not same chap as the 1802 born one. That said, the Leitch/Sinclair marriage, on checking original, does have an age column, and against Archibald says 'full', so no clear indication of his actual age and if he was the 1804 born chap.