How Long does an even survives.

If not caught, how long will an even linger around?

I am generally using a code like the following to do stuff:

while true do
e={os.pullEvent()}
if e[1]=='rednet_message' then
--do stuff--
end
if e[1]=='timer' then
--do stuff--
end
if e[1]=='monitor_touch' then
--do stuff--
end
end

which works fine in most cases. But if we imagine a situation where the part after pullEvent takes a longer time, I suppose it will be possible to miss events. How long, for instance, a key press remains as an even that can be caught? Also is there a way to put events on hold while having the computer do other things?

Events are stored in a queue. You won't miss them unless you overflow the queue stack.

Explanation:
Say there are two keypresses. The queue is now

key = keys.enter
key = keys.up

Then the code does os.pullEvent(), getting the first key event. The queue is now

key = keys.up

That key will continue to wait in the queue until another os.pullEvent or os.pullEventRaw is pulled.

Be alert to the fact that a good many functions provided by the CC api's pull and discard events until they get a specific type. So for example if you do a rednet.receive() or a read() to get some string input, all the events other than the "rednet_message" or "char" events needed by those functions get pulled and discarded.

Yeah, but for example if you use rednet.receive(), you obviously are only interested in rednet events, so there's no point in keeping all the other events is a queue. (that is certainly possible however)

Meh, sometimes people want to get all the events but forget that a particular function discards them.