To find out when Bernard Irons 2 was discharged you need to go back to the muster books and follow his service to the end. It should give an explanation as to why he was being removed from the list - either he died; or was discharged; or he was transferred to another regiment, in which case you have to follow the musters for the new regiment.
If you are basing the belief he was alive in 1845 from the fact he is not described as deceased on a marriage certificate that cannot be relied upon 100%. If you have the certificate you may need to check the parish register, and vice versa. The next bit requires a bit of lateral thinking. If they are the same person he would have been entitled to the MGS (Military General Service) medal for the battle of Vittoria (on that date in 1813). It was authorised in 1847 and men had to be alive then to receive it. There are no Bernard Irons listed in the roll for either the 66th Foot or 41st Foot, so if they were not the same man (and No 1 was dead), and No 2 did not fight in Spain/France/West Indies; or they are the same person and he was dead before 1847.
If you can also find from the musters when No 2 had served 7 and 14 years, they usually include extra information, such as where he was born etc. No 2’s record is not in Kew, and if he died in service the War Office would have destroyed it 20 years later.
Also, are you saying he was a Sergeant in 1816, when he would have been 21? That would be a bit young, but not impossible.
Regarding the family, you should check the overseas/regimental BMDs on Findmypast etc. These started before civil registration. Otherwise you have to research the musters for the length of his service, and then search the church registers of the places he passed.
Did you check to see if a soldier of the name Doorley/Dawley had been in the same regiment? It was quite common for a soldier’s widow to remarry within the regiment. Finally, registration of protestant marriages started in Ireland well before civil registration started in 1864, so you may wish to look at this.
Ken