BIG HUGS
I am so very sorry for you sudden loss. When piggies get to a grand old age like Speedy and her mate, unfortunately when the end finally comes it often happens very suddenly and quickly in my own experience; in roughly half the cases I have to emergency pts/euthanize. Which way it goes and when it happens you can never choose or predict because it ultimately depends on whether an organ gives (in your case most likely either the heart or the gut itself) or whether it is the immune system that is breached; but in the real oldies it is often like a house of cards falling down because of the general frailness.
I just try to treasure evey day over 5 years in my normal adoptees and over 4 years in my adoptees with a potentially compromised background and to feel blessed every morning they are here to greet me.
What you want to do depends on whether you want to continue with guinea pigs or not.
If yes, then you may want to consider adopting a next door pair for companionship and stimulation through the bars but give your remaining old lady the freedom to choose whether she wants to join in or not; many old ladies won't necessarily but you can never predict that.
I've currently got a determined 6 years old single widow again (with a pair of younger siblings next to her as the ones she is getting on best with - just not in her own space) but I have also had piggies your age who have happliy accepted a young baby sow or two into their group and lived for another year thanks to the renewed zest for life or who bonded with another older sow (although that took some time unless they knew each other from previous times). Some of mine have accepted a neutered boar; others not...
There is no surefire way; whatever you do make sure that you have a plan B (next door companionship).
You may find these links here helpful in exploring different aspects and working out which way forward may be best for you. A lot depends on your personal situation, longer term plans and local availabilities. I have included helpful advice for keeping singles as well if you do not want to continue with piggies.
Death, Dying, Terminal Illness; Human Grieving and Bereaved Companions: Information and Support for Owners and Their Children
Caring for Older Piggies and Facing the End - A practical and supportive information collection
Single Guinea Pigs - Challenges and Responsibilities
Moody Guinea Pigs: Depression, Bullying, Aggression, Stress, Fear and Antisocial Behaviour
Rescues (Adoption and Dating), Shops, Breeders or Online? - What to consider when getting guinea pigs
Adding More Guinea Pigs Or Merging Pairs – What Works And What Not?
Bonding and Interaction: Illustrated social behaviours and bonding dynamics
