Any Type of Allergies or other conditions should be ruled out before a dental extraction. I Dont see any problem apart from that. Get your Tooth fixed as soon as possible.

your tooth can be saved only if there is some required amount of structure left.. also sometimes there are some conditions in which it is difficult to retain the tooth.. better consult ur dentist.. he will guide better.

Search for a dentist in your vicinity using Practo and try to make a visit as soon as possible so that the current condition can be evaluated properly and the right treatment can be suggested there after. There is a possibility of the tooth being restorable and the need for extraction can be avoided, and if that happens it will be considered as the best approach. If the extraction is not avoidable, the replacement options are also multiple and can be discussed according to the condition of the remaining dentition. Regards.

Yes of course it's necessary Because if in future that decayed tooth gives you pain nothing can be done without removing the replaced tooth