>>> if he hasn't used all the fiver's worth, is that lost, and they then take another fiver?
"Yes" . . . and possibly/probably "yes".
You seem to have set up the
wrong type of PAYG account. There are two sorts, which I'll try to explain below:
1. When PAYG phones first came onto the market, people paid to buy (fairly expensive) credit whenever they felt that they needed it. (i.e. there were no monthly arrangements). Such credit lasted indefinitely, except that it was necessary to make at least one chargeable call in a set period (which was often 180 days) in order to keep the account active. (If no such call was made, the number would be disconnected and all remaining credit lost). I'll refer to this as 'raw' credit below, for simplicity.
2. At a later stage though, phone service providers introduced the concept of 'bundles'. (Some companies have their own names for 'bundles'. GiffGaff, for example, calls them 'goodybags', while EE simply calls them 'packs'). When a user buys a bundle, they get a certain number of minutes and/or a certain number of texts and/or a certain amount of data for a fixed price which can work out much, much cheaper than using 'raw' credit for anyone who uses their phone regularly. The downside though is that, while 'raw' credit lasts indefinitely, 'bundle' credit only last for thirty days, with any credit unused at the end of that period then being lost.
People using bundles aren't obliged to automatically buy another one at the end of 30 days but most people choose to set up an arrangement whereby payment for a new bundle is automatically taken when the preceding one expires. If you've set up such an arrangement, then your friend will get a message in thirty days time, telling him that EE are about to take a payment from his bank account and then, a day later, another message telling him that they have. If you've not set up such an arrangement, he'll simply get a message advising him that he needs to buy another bundle (or, as EE calls it, 'pack') in order to keep his phone service active. [Hence the 'possibly/probably' bit at the top of my post. It's not entirely clear to me what you've actually done].
If your friend definitely only wants his phone for emergency use, it would be better to switch to an arrangement that uses what I've called 'raw' credit. He'll then get charged a staggering 35p per minute for his calls but (as long as he makes at least one call every 180 days), his credit will never expire.
Even when using 'bundles' (= 'packs'), it's always wise to have some 'raw' credit on a phone anyway, as 'bundles' don't include things like calls to premium rate numbers. So there's no reason why your friend can't add some 'raw' credit onto his phone right now, to run alongside the 'bundle' you've created. He can create and top-up 'raw' credit using any of the methods shown here:
https://ee.co.uk/help/help-new/billing-usage-and-top-up/topping-up-and-balance/how-can-i-top-up-my-phone
(If you've set up a recurring bundle arrangement, he can cancel it by calling 150 or simply by texting 'STOP REC' to 150).