c# - SQL change static connection string if there is no connection -

i have static class, return connection string like:

public static string cstring() {      //(...)      string connstring = string.empty;     //check if have read connstring file or use static connstring     if(readconnstringfromfile)         connstring = "...";     else         connstring = "...";      return connstring; } 

so anywhere in application im creating new connection server like:

using(sqlconnection conn = new sqlconnection (cstring.connstring)) 

i have 2 databases. if application lose connection main db, i'd change connectionstring second one. possible (for example in app.xaml.cs) check connection database , if doesnt response change it? if possible, how overload application? need best method, wont overload much, becouse pc's quiet weak.